very few games are CPU limited, unless you are planning to play GTA IV and FSX a lot they will perform very similarly and the bottleneck will fall onto your graphics card. If you are going to be spending a lot of time playing GTA IV or FSX the i7 will do better as it is a stronger processor, but for normal games they perform very similarly, but i suggest a 955 over a 965 as its cheaper and has the same OC potential.
I would suggest against an intel motherboard, yes they are super stable, but they dont give you many options if you want to OC at all. If you arent planning to OC the stock fan will do quite well, if you are the cooler master 212 actually does extremely well for the price http://www.newegg.com/Product/Product.aspx?Item=N82E168...
I would go for the XFX card as it has a lifetime warranty if you register it in the first 30 days, and if it dies the extra for that warranty will definitely pay for itself.
I5-750 @ $200
Overclocks better than the i7 920
P7P55D-E PRO @ $180
Supports PCIE 2.0 x16 for one card, if two cards are in the slot it becomes x8 for both, however the 5870's will not be bottlenecked by x8
One of the best overclocking friendly motherboards i've seen
SATA 6GB/s and USB3.0 unhindered support
or your other options
i7 920 @ $280
Hyperthreading (doesn't really help in an overwhelming amount of games)
DX58SO @ $230
Supports full PCIE 2.0 x16 on crossfire/sli
No USB 3.0 support or SATA 6GB/s support
Phenom II x4 955 @ $166
AMD motherboards @ $110-170
No USB 3.0 or SATA 6GB/s support
well there it is for the most part, and btw good choice with the 5870 i have a 5850 from asus and it works great, I can only imagine what one let alone too! will do.