I have an i5 750 on an Asus P7P55D PRO mobo, and it's really good. My cooler is a Zalman CNPS10X Extreme which is really around the performance of a 212+, and I achieved 4ghz fairly easily. Took me 1.32Vcore and 1.25VTT iirc, temps tho were starting to hover around 70 in a burn test. Currently running 3.68ghz with turbo on, so single core gets up to 4.2ghz and the temps are way lower, like low 60s. I prefer the turbo boost OC, actually, since not only is it lower voltages, and cooler, but for gaming you usually only use 1 or 2 cores so the speed is still 4 to 4.2ghz.
As for the PCIe stuff, the MSI P55GD85 cannot have two 16x lanes because, as Raidur points out, the 1156 socket CPUs don't support that. They have 20 lanes, 16 of which go to the PCIe lanes and the other 4 are for other things. Some mobos like my ASUS have a 4x PCIe lane, but it's actually running through the south bridge so it's more like a PCIe 1.0 lane I think. Something like that, there's an article on Tom's the shows it performs quite a bit worse than the X58 chipset (i7 9xx CPUs) 4x lane because in that case it's a true 4x lane directly connected to the CPU.
Anyway, 8x lanes are totally fine although I think a 480 would lose more than 8% since in Tom's article that I mentioned above (something like X58 vs P55) a 5870 lost 4% on the 8x lane... but regardless he is right that a 460 will see very little to no difference in speed.
Just one last thing about the mobo, I had an MSI P55GD65. While I did like the board and it's features, it ended up dying on me after only 3 weeks. I brought it back (and got it replaced with the ASUS) and the tech told me that they've actually been getting quite a few MSI returns/faulty boards so I personally wouldn't get an MSI board for this generation.