A lot of people, I have read, say that 1200-1250 shadow/fire damage (depending on fire or shadow destro - which is where you're at based on your armory that is linked in your sig that no one has clicked) is a good point to start stacking haste. However, I would also suggest taking a look at Leulier's spreadsheet, plug in all your info, and see what you come up with. If all else fails, there's also personal dps testing on Dr. Boom, too.
Edited, Jul 7th 2008 2:14am by wingsofscion