^ Yes. The Corsair 750 will be enough for 2x 5850s in CrossFire.
Spend a little more and grab the GSkill Ripjaws. You can also drop down to a X3 for gaming use and save some money.
WAY too much money on the heat sink. Get a Hyper 212+. If you want silence, spend about a $100-120 more and go water cooling (which is a better investment imo if silence is golden to you).