However, the requirement on the mystical skyfire gem makes it unsavory, at least until a stage is reached where it is possible to hit cap without using +hit gems. Which means the only other gem it really compares to right now is either the +12, or the +14 damage meta.

Ok, I killed a bunch of Worg's in Terokkar with +857 Fire Damage spamming Flame Shock only, this is what I got:

588-589 Non Crit
1229-1230 Crit

This is what wowwiki says about the spell that Elemental Shaman's use ~99% of the time in raids, max rank has a 2 second cast time with talents and gets 85% of our Spell Damage bonus so this gem seems to be very good, for Shamans at least http://www.wowwiki.com/index.php/Lightning_Bolt

@galzohar, the 5% half cast time gem would cut LB into a 1 sec cast but because of the GCD I'm not sure it's worth it for a Elemental Shaman using the Engineering goggles for example.

Okay, quick and dirty maths before falling asleep!

Suggestive's data: Immolate hits - 712 - 713, Immolate crits - 1488 - 1489
1488/713 = 2.086956, 1489/712 = 2.091292

Oprahwinfury's data: 588-589 Non Crit, 1229-1230 Crit
1229/589 = 2.086587, 1230/588 = 2.091836

[top]> It makes your crits go from 200% to 209% crits, the bonus goes from 100% to 109%.
This makes crit 9% more useful than it is right now for damage, so if you had 1 crit rating

0.8 dmg before, you now have 1 crit rating = 0.8*1.09 = 0.872.

How does that work formula wise when a spell that hits for 100 damage crits?
Perhaps (100 + 50*critmod_talents+1.03)*1.03?
It would be 209.09, which is between our upper and lower borders from your numbers.
Isn't exactly the same how the hunter numbers work, sadly.

So, anyone with numbers how it affects spells that crit for 150%?

Yeah I already mentioned I did the numbers for frostbolt and fireball. Granted for lightning bolt it'll be less:
1 in every 20 spells is 1.5s instead of 2s - you get 20 spells in 39.5s instead of 40s - 1.2% cast speed increase. Still more DPS than the extra crit damage trinket probably, but you'll have to math it out, and for lightning bolt it's actually close enough to not bother with its requirements of more blue than yellow and the fact it doesn't give any efficiency.

Yep interesting you're not supposed to get 209% damage crits even if the meta is working. I'd look into any error that could've cauased that (such as - did you average your damage over time or just looked at how much it hit for)?
If you really crit for 209% I'd really appreciate it if someone can post a reasonable explanation for this ;p

Suggestive's tests suggest (sorry) that it is 209% as well. I'd say it's probably bugged in it's current form, enjoy it while it lasts.

I already had a Relentless made and ready to test with, but having the minor problem at the moment of not being able to get my t4 helm token to drop to actually plug it in to. If it's 209%, that's insane... will definitely wish harder for the token next week's Prince. Even at 203% it would be the best metagem as per my maths above (because reducing LB to 1 second is defeated by the global cooldown anyway). At 209% it's 5-6 times better than the 14 spell damage metagem.

Test from a guildy with untalented Arcane Missiles (no crit modifiers):
598-599 hits. 924-925 crits
924/599 = 1.54257, 925/598 = 1.54682

Looks exactly like 150%*1.03, a flat 3% increase of the final crit damage.
We had the same result with fire (Molten Armour 89 hits, 138 crits, but the damage is too low for exact predictions).

So, we have a normal effect on spells without crit damage modifiers, but an increased effect on spells with crit talents.

Looks like the resilience issue to me, that the crit talents apply to a pretty odd number for the crit bonus damage:

C := {(150%*1.03) - 100%} is the difference between a normal hit (100%) and a crit with the crit gem and no crit modifier talents (150%*1.03).
(( Resilience works the same way, with the resilience modifier (0.9 for 10% crit damage reduction) instead of the listed number 1.03 (crit gem). ))

The final damage for a crit seems to be (it fits all test results and fits the resilience problem)
100% + C*(100% + crit_talents).


So, for spells without crit talents we get 154.5% crits, for spells with a +100% crit talent (elemental shaman, balance druids, destruction warlocks, frost mages) we get 209% crits.
Arcane mages get 181.75% crits, arcane/frost mages get 236.25% crits, fire mages (Ignite is no crit modifier but just multiplies the total damage done by 1.4) get 216.3%, arcane/fire mages get 254.45% crits including ignites.

My final thoughts - it's much better than the spirit shard gem, not as good as the half cast time gem. The latter one has a stupid gemming requirement and can mess with spell timing (I have it on my T4 hat and it's really really fun!), so I'll probably have +12 agility on my next hat :o

Doesn't arcane/fire (spell power + ignite) get 1.75X1.4=2.45 crits? How come it's 2.4545 with the gem? did you mean 254.45? Fits your theory much better looked like you just swapped 2 digits ;p
So for a 33/28 mage this would be the same DPS increase as increasing crit chance by 3.591 if you have 38% crit in full buffs, which is equivalent to 79.3 crit rating or 58 spell damage.
Same math for 10/48/3 makes it worth 38.7 spell damage. For comparison the 5% chance to 1/2 cast time is worth 2.5% haste which is equal in terms of DPS (but not DPM) to 51 spell damage with my gear (~1250-1300 spell damage with full buffs/pots/etc). Not to mention the extra damage you can get by not matching the requirements brings the crit gem to the top of the list of mage gems.

What I really wonder if the effect on spells is intended or not (seeing the 12 agi on it...)
Don't really want to get that gem just for it to be "fixed" the patch after...

Tested with a few hundred frostbolts ageinst lvl 1-3 mobs around northshire:
Non Crit dmg from 1518 to 1568.
Crit dmg from 3173 to 3275 wich is clearly 209%.