Yes, your sample size is way too low to distinguish 2.1% vs 1.2%. This is especially
true as this is a sample size over different bosses that may or may not have frost
resistance mucking things up.

There are statistical techniques that will tell you how big a sample you need to
have a 99% confidence rating in the result and the deviation you can expect for
a given sample size. I was going to get all geeky and work it out but I'm rusty
by about 2 years on it and my license for my fancy statistics tool expired so I'm
afraid of giving out misinformation.

So the following is conservative, based on hazy memories of trying to distinguish
similar variances in quality projects:

For a good test, get a tank and healer, find a L70 raid boss they can tank pretty
much forever and spam frost bolt 1s. Get a sample size of at least 500 and
that's probably good enough to distinguish a 1% shift with reasonable confidence.

If you're trying to distinguish tenths of percents, you'll need more like 10k.

Hi, I am currently equipped with 4T6 pieces, 1156 dps with 28.27% fire crit and 8% haste. Almost all my gemming is on spellcrit+spd. Also I must mention that my gear is not fantastic and I am missing a few (in my opinion) crucial items (like Head piece and trinket from Illidan, as well as Tempest of Chaos and offhand from MH), but I am just unlucky, so I have to play with what I have.

I was "raised" with notion that crit is the most important stat (after capping hit) for a fire mage, and should start on 30% (unbuffed). When haste was introduced, I tried to balance spellcrit and haste, but prefered to get to around 30% before working on my haste.

Since recently I have been hearing from mages on my serv, that I should change gemming to forego crit in favour of haste. Any advise/opinion on this?

thanks

This should really go in http://elitistjerks.com/f31/t16781-mage_help_me_please/, but the mages you've been talking to are correct. Gemming for crit is about the worst thing you can do, since point-for-point, it takes far more crit rating to earn 1% crit than it does to earn 1% hit or haste. You don't want to completely ignore crit, but we get plenty of it on our gear anyway. You will get a much better return by gemming for haste or pure spell damage.

As it stands right now, is there a popular school of thought with regard to what the two best trinkets to use are?
I see a LOT of mages using skull + head, but wasn't sure if that was just what they felt were the 2 best or of there was some reasoning behind it.

Bringing it up here for sake of it being mentioned as an issue in the original post.

From what I'm aware for 40/0/21 the 2 are SCB + Hex for the specs ability to stack all of it's CD's at once along with it being a very mana hungry spec making the SCB's benefits 2 fold. But I'm not aware of there being such a clear cut pair for Fire.

The answer is "it depends on your gear and spec" and to some extent "on your behavior"

As an example, a trinket that procs on randomly works better on a spec that casts lots of fast casting spells than lots of slow spells with moderate crit rates..up to the point where its internal cooldown makes the more frequent procs irrelevant. Stuff with +spell damage for limited time works better if you have talent-based cooldowns to stack it with...assuming you actually make use of it at the right time. If you are low on spell hit or run out of mana, some trinkets are more attractive. If you have trouble with on-use trinkets, using them properly, a trinket that randomly procs or just has a lot of raw spelldamage and no clicky thing might be better for you. If you die a lot because of low stamina and can't fix this with behavior, a stam trinket might be better than a DPS trinket.

This site:

Man Out of Time - Theorycraft-o-Matic

Will let you enter your stats and will rank trinkets in order of how much DPS they give you. The output is fairly good if your input data is ok, but there are some assumptions about rotations and behavior that may not match yours. It assumes a well played mage with good rotations, one of the standard raid specs and well timed cooldown use.

I don't know if it has had the review of RAWR, but it seems pretty good and is where I would go first if I had no idea what might be useful for me.