2 crit > 1 int (always)
2 crit > 2 haste (always)
2 haste > 1 int (under 3056)
2 haste < 1 int (over 3056)
To be clear, you never ever gem haste.
Just as mrgreenthump responded to Silentbob, often times with current gear set up, when you gem more hit, once reforged, it actually ends up being more haste.
This is because, once over hit capped, a gear piece with: crit/hit will reforge the hit into haste, or a piece with: crit/haste that would have originally reforged the haste into hit no longer does so.
So, where this comes into play is the red socket. If you're still trying to reach 3056, you gem expertise/crit, and after reforging, you should come out with more haste. If you're over 3056, then the red socket should be int/crit.
https://docs.google.com/spreadsheet/...ZmFYa0E#gid=39
3056 is the number while raid buffed will get you 14th tick NT and 23rd tick Glyphed Combustion. The corresponding haste without 5% haste would be 5334. You won't be able to reach this without sacrificing a lot of crit... so don't go for it.
3175 however is the haste for unbuffed 22nd tick of Glyphed Combustion. You might want to try to go for that, but of course, never sacrificing crit.
---------- Post added 2012-10-24 at 11:20 AM ----------
You never move on to haste, you reforge to crit as much as possible. When you reforge into haste is with a piece of gear that already has crit and another stat on it.
1: crit/mastery - reforge mastery into hit if under cap, to haste otherwise
2: crit/hit - reforge hit into haste if over the cap
3: crit/haste - same as 2, but reverse
4: haste/hit - reforge haste or hit into crit (depending on where you are with the caps)
5: Mastery/hit - reforge mastery into crit
6: mastery/haste - reforge mastery into crit