Should have dropped into the systems forum, we could have made a good build for you.
A gaming rig usually has 8GB of 1600Mhz CL9 RAM. I recommend this kit since its low profile, so large heatsinks wont be a problem.
G.Skill Ares 8GB (2x4GB) 1600Mhz Cl9 1.5v. $44
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231544
For Intel processors, you cant have RAM that runs above 1.5v, otherwise it puts the memory controller under more strain than was intended. Shortens the lifespan of the chip and (not sure on this) void the warranty. On an AMD system there's no restriction on voltage though.
Sandy and Ivy Bridge are pretty similar. Sandy Bridge is an architecture, how everything is sort of arranged inside the CPU. Ivy Bridge is a die shrink of Sandy bridge, so some small tweaks, newer technologies and a smaller manufacturing process. Basically they can fit more transistors into the CPU with a lower power draw plus some new features.
Intel strategy is called Tick-Tock, Sandy was the Tock, which means a new architecture. Ivy was the Tick, a die shrink.