I think this haste debate is getting a bit too deep. Are people really thinking of reforging before every single fight?
Of course, haste is the only thing to consider reforging out of / into on a semi-regular basis. This is because it's the only one that actually affects playstyle (you adjust how many chaos bolts you can cast during procs) and can end up making certain bits of certain fights easier. On the other hand, because of the playstyle change it's probably better to keep haste as your most static stat, because you get into habits of knowing how long a cast will take, and it can bite you on the bum if you're not used to your haste rating and you miss a big CB.
Personally I've just decided to settle on 8100 haste for when I offspec demo. Mastery is overall the best stat for the class so I gem / reforge extra hit into mastery. Reforging into / out of crit is unnecessary.
AFAIK the only reason people reforge completely out of haste is because they don't like an LMG proc / heroism causing their incinerate to be a shorter cast than the GCD, which is fair enough. It really is just preference.