Stick with the i5-750. It's arguably the best gaming CPU out right now. I just went from a 790X Phenom II 955 build to an i5-750, and I'm very impressed at how well everything performs and overclock's etc. I'm running at 4Ghz on air with moderate 1.3v vcore, I could never get my 955 over 3.7 stable...even with a 1.5 vcore. Also, most DDR3 1600 memory is made for the 1156 chipset, so you get better compatibility across the board that way. ASUS are generally viewed as the best mobo's, but I've had good luck with an inexpensive Biostar (99 bucks at Fry's after MIR.)
For some reason, Intel's mainstream chipsets only support PCI Express 2.0 on the primary links that are used for graphics. This applies to both LGA 775 and LGA 1156 platforms. While Intel claims PCI Express 2.0 support for its LGA 1156 based PCH, it limits throughput to PCI Express 1.1-class performance. This is naturally a problem when we start looking at the latest high-speed motherboard-down controllers.
AMD, on the other hand, upgraded the link speeds on its 700- and 800-series chipsets, which means that current AMD mainstream and enthusiast chipsets don’t create bandwidth bottlenecks for high-speed add-on devices."
If you are not going to crossfire, it's not going to be a big issue. If you are planning to crossfire and want to utilize USB 3 and SATA 3 also, then it could become a bottleneck.