There is none. When you feel comfortable with your mana pool and you find more pieces of gear with haste on them, you can begin to switch out. However it's not worth it if you don't reach the next haste breakpoint. So only switch out when you're sure you can hit the 2005 break point for an extra riptide tick.
However, I don't recommend it in this patch and I doubt Myrev will recommend it either. If you know what you're doing however, go for it ^^
edit; Basically, you can't have more haste without losing a lot of other stats. Personally when I'm comfortable with my mana pool I'd switch out some crit for mastery to help with the heroic raids.