A 9 damage gem and a 8 hit rating gem give an obvious total of 9 damage 8 hit.
2 5 dam / 4 hit gems give 10 damage and 8 hit - same gem slot count and more damage.
To be honest you should never really be at a gear level where 8 hit gems are needed for hit cap, so if you run into the "what should I swap my 8 hit gems with?" question you already made some gearing mistakes it's all about if you're willing to replace double the amount of gems in order to gain 1 spell damage each or not - but if I had 8 hit gems in my gear I'd feel bad enough to take the time to farm the gold and fix it
If you're doing good with a bad spec (not to mention bad gear) then you're not really doing good, it's just the people you group with are that much more terrible and you can do that much better.
I don't see why you connect fire with going oom and arcane with not going oom, it's the exact opposite, with arcane always going oom due to spamming AB to get any reasonable DPS while fire can only spend as much mana as fireball costs. Your extra int and regen from the arcane tree are a joke when compared to the mana inefficiency.
Yeah arcane will AOE better but to be honest even on morogrim the fight will probably be decided more by doing a bit more DPS on him than doing a bit more DPS on the murlocs that get mowed easily anyway.
I connect fire with going oom ONLY when doing heavy aoe dmg, since I don't have 2pc t-5 I wasn't (and I may be wrong) spamming AB I was a arcane/fire spec keeping up my scorches and spamming Fireballs in between waves.
The question is how much gold do you have to spend on them, since most of these are a tad pricey. The Runed living Ruby's are relatively innexpensive (abt 50 gold on my server), compared to a few hundred each for the better ones. So that is likely your best bet, unless you have thousands of gold to spend.
Edited to correct the description's of the gems listed.
MagePryde: Like another poster I assumed wrongly you were in fact advocating 33/28/0 rather than the 28/33/0 you're specced currently. There is no logical reason behind speccing it, indeed, you're missing extremely fundamental talents of both hybrid arcane-fire and full-fire typical specs. Many of your talents could be swapped for a dramatic improvement, even at your low gear-level. Everything in Arcane (except perhaps Presence of Mind) past Arcane Concentration is worthless. It's debatable whether there's a point to Arcane Mind, given you're probably mashing Fireblast to improve on your dps. From fire you've missed out Imp. Scorch, which is needless to say, is between 12% and 15% more DPS on a boss-fight. You've missed Molten Fury, which is the whole point of Fire and Pyromania, as well as Empowered Fireball which is probably the most fundamental fire talent after Molten Fury.
Looking at the rest of your gear also indicates sloppy and hap-hazard itemization. You lack a glyph on your head, a patch on your pants and an enchantment on your shoulders. Your weapon, gloves, boots, chest and bracers are enchanted with junk that does not help you as much as it could/should. Your gemming is mostly random and your overall hit rate is bordering on deadly-low.
Priorities for you, are in order of importance:
Read well the first page of this thread. It is by no means wholly accurate, but for your playing bracket it is exceptionally well-written and informative. I don't say this to demean, I say this because I honestly think there's knowledge about being a raiding mage you are not taking note of. The fact that the first page may not reflect the exact, up-to-date conditions and situation of mage T6+ raiding is irrelevant to you.
Decide on a well-established spec for you to follow (at this point in your raiding, any pure spec will work fine. Full Frost (10+/0/42+), Full Fire (2/48/11 or 10/48/3), Arcane-Frost (40/0/21) or Arcane-Fire (eg.40/18/3) only selecting talents you understand will increase your DPS. Prismatic Cloak, Blazing Speed, Imp. Mana Shield and other junk does not make you output more. This is why we call them "fillers" and avoid them like plague. It's fine speccing them for when you can't get anything else, but it's not when you skip fundamental and obvious talents like Pyromania, Molten Fury, Imp. Scorch, Arcane Instability, Spell Power and Arcane Power.
Max your tailoring, get all BoP epic tailoring gear of either frost or fire/arcane. Get appropriate enchants/patches/glyphs for your gear. Tune your gems to be hit/dmg till you're hitcapped (124 frost 164 fire, both assuming you spec Elemental Precision and there's no excuse not to) and not random mish-mash of penetration, int etc.
Understand what you're lacking and hunt items to suit: You need Hit rate more than anything else to compete in a raid past trash, and you need a lot of it. Belt of Blasting, the gloves from Attumen, the Cenarion-rep Exhalted ring and the Scryer's revered Trinket will all make you much more effective at raiding.
I am well aware of how bad my 'magery' is. I have been trying hard to get better at it and do what needs to be done to outshine the warlocks and other dps casters in kara (being i can't sheep anything =( ). To be honest i don't have a clue as to why i didn't go with imp. scorch, and i'm fairly sure i took mana shield as a filler to get arcane med. Thanks for the help, i really do appreciate it.
Karazhan is the BEST ZONE because you CAN'T sheep anything. Trust me. If I could go an entire raid night where the officers were like okay mages, just sit back and cruise on this trash, pew pew pew, I'd cry of happiness.
After about a month of inactivity due to lack of certain classes, my guild has been able to rise from the ashes and start doing some real progression. As soon as we had the correct numbers we 1-shot Leo (SSC), skipped TK, 1-shot the first three Hyjal bosses, and wiped 4 times on the first BT boss because idiots couldn't click the spines fast enough (we did kill him 5th attempt though). This was done in roughly 1 week (over 3 raid days).
I'm always in the top 3 dps, usually sitting 1st or 2nd (with my deep fire build). I like being on the very top, but I don't see this lasting long due to people gearing up and learning how to maximize their dps during the fights. Here's my current wishlist:
Is there something I should be changing about this? Maybe an item I'm missing? I have T5 pants but I don't even think it's worth replacing spellstrike at this point even with hood of hexing because I'm already hit capped.
EDIT: I will actually be OVER the hit cap by 28. I can take off 10 hit rating from gems on my spellstrike set but that still leaves me 18 points over the cap. Suggestions are GREATLY appreciated.
Zooch: I'm not sure what the point of your post is as you don't ask any questions. Anyway I disagree with your gem choice for Hatefury Mantle. The socket bonus is awful so you might as well stick 2 +12 damage Crimson Spinels in.
Not actually a member of Refusion on Burning Blade.
Well I would really prefer to replace spellstrike if you have any suggestions. I dont see the slippers being a huge upgrade from my current boots - what am I missing there? I know I'd be exchanging crit for the hit I dont really need, but the spell dmg would be the same and Stam/Int/Spi would all suffer substantially. I'm at like 7700 health unbuffed too (it's about 10.2k raid buffed).
If this matters - 90% of the time I have a shadowpriest and shaman in my group, 50% of the time elements is up.
Actually I misread which boots you had which didn't help (thought it was a pair from Kara). Spellstrike legs can be replaced with the badge ones ([Corrupted Soulcloth Pantaloons]) or [Leggings of Channeled Elements]. Not really any options for T6 level head until you've killed Archimonde and/or Illidan. T5/Cowl of the Grand Engineer are the alternatives.
I'd also definitely replace all gems with hit if you're struggling to stay under the cap. Pure +damage or +damage/haste would be better.
Not actually a member of Refusion on Burning Blade.