Quote Originally Posted by Noids View Post

What I like about mastery is that 1% mastery will mean your nukes (not including ES/fulmination) will hit 1.5% harder on average. Getting kills in PvP is all about having heavy nukes and this is the best stat to achieve this. 1% Crit will only give an extra 1% to nukes (not including LvB). Sure haste will let you get more spells of in a short period of time, but this is only if you are allowed to stand still and cast. Even if this is the case, again you will only increase your total output by 1% per point of haste rather than the approx 1.35% from mastery (averaging damage from spells affected by mastery x 1.5%).
Not really sure what numbers you're using, but 100 haste increases your casting speed by 3.05%, which means your damage and healing output is up by 3.05%, and you don;t have to stand still as long to cast your spells. 100 mastery rating increases percent chance to fire another nuke for 75% damage by 4.36%. Even if 100% of your damage came from nukes, which it does not, that is only a 3.27% increase in your damage output, and your time to cast these nukes is not faster.

100 Haste increases damage AND healing by 3.05%
100 Mastery increases (theoretically) just damage by 3.27%

For PvP, trading in that small amount of damage increase for an increase in healing potential is a pretty good idea.