Where are you located / where are you buying from?
Ignore the OCZ unit.
HX 750 V2 is powerful enough, it has 4x 6+2-pin PCI connectors so it supports dual 8-pin graphics cards. Your 7870's will use two 6-pin connectors so there will be plenty of power overhead for connecting the GTX 650 via a molex-PCIe adapter. I'd estimate your gaming load power consumption at around 500-550 watts.
Compared to AX850, HX750 is probably a lot cheaper but there's not much difference between them apart from that. Both are highly efficient, modular and with 7 year warranty.
Asus P8Z77-V | i7-3770K @ 4.2GHz | Scythe Mugen 2 with Noiseblocker B12-3 @ 5V | 2x4GB Samsung 1333 | Sapphire 7950 1100/1450 | Asus Xonar DX | OCZ Vertex 2 120GB | Samsung F4EG 2TB | WD Caviar Green 1TB | Seasonic X-660 | Fractal Design Define R3 | Bitfenix Hydra Pro with Noiseblocker B12-3 fans | BenQ XL2411T | Sennheiser PC350 | Logitech G710+ | Zowie AM-GS | Zowie G-TF
Last edited by lehtv; 12-20-2012 at 06:26 AM.