|Personally, I suggest you get at least two PCI express slots. Try to find a motherboard that has PCIe 2.0 (16 lanes) at least. I haven't seen many 3.0s on the market, and although they exist, they tend to be expensive. Generally, using a graphics card with a 3.0 in a 2.0 slot will only give you about a 5% performance hit, as most cards can't really use most of the bandwidth provided by 3.0. (So long as both are 16 lanes, 8 or 4 lane 2.0 will give you considerably less performance) It really just depends on the card. |
In the past, I have had better luck with AMD graphics cards over Nvidia, although really it is just a matter of personal preference, both make very good cards.
Getting two slots in the mainboard might seem like a waste, but you have to remember you can always buy another card, then connect them via either CrossFire or SLI to give you increased performance.
You also might consider getting an APU, which is a CPU + a graphics processor.
For RAM, I would suggest getting a motherboard with four slots. Two is doable, but doesn't give you much headroom for upgrades in the future. At the moment, most games only require about 4 GB of RAM, and I doubt any next-gen games will need more than 8. Personally, I got 2x4 GB of RAM, and plan on upgrading to have 2x4 + 2x8 in the future. If you get a mainboard with only two slots, you should probably get one 8 GB card instead of two 4 GB cards, so you can upgrade later without wasting your money later. Technically, having two cards (called dual channel) does give better performance, but it really isn't noticeable.
I suggest getting either 1600 or 1866 DDR3 RAM with a good CAS latency of about 9. For the most part, this is about all any mainboard or CPU can really fully use. Some CAN use higher, such as 2133 or 2400, but for the most part these are just factory OC'd cards, which you can do yourself.