+1...Even though I've ran dual 4870s on the 750TX which in theory draw more than the 285s, it never hurts to have extra power. I'm always leary of the newegg reviews, I would say at least 50% of the complaints come from user error on any given product....my point to the OP was that he ALREADY has the 750, and I'm not sure if he can still return it, so I think he will be alright with it if he adds another 285...if not you'll know when the power drops you'll need to get a new PSU.
Dual 4870's draw less power than dual 285's.
4870 = 450w min PSU with at least 36a on the 12v
285 = 550-600w min PSU with at least 42a on the 12v
Unless I missed something here, IMO the 285 is more powerful and more of a power hog than a 4870..