RAM: 12GB 1600 or 8GB 1866

12gb for triple channel ram on a LGA1366 system or 8GB in dual channel for all other modern systems that run in dual channel regardless of the speed difference posted!

For a dual-channel gaming system, I recommend 8GB (2x4GB). Two or four sticks is best for dual-channel.

For a triple-channel gaming system, I recommend 6GB (3x2GB). Three or six sticks is best for triple-channel.

DDR3-1600 is a good speed to get. CL9 is standard. Get CL7 or CL8 if you want to spend a little extra. Oh, and make sure it's 1.5v spec RAM.

Thank you very much!

To add, it depends on your MOBO. If you're building a P67 rig then 1600 CAS 9 is the sweet-spot. And there is an advantage to 8GB, plus RAM is cheap... Obviously, use a 64-bit OS.

Good articles -
Sandy Bridge RAM http://www.bit-tech.net/hardware/memory/2011/01/11/the-...
Gaming 8GB+ http://www.tomshardware.com/reviews/ram-memory-upgrade,...

G.SKILL Ripjaws X Series 8GB (2 x 4GB) DDR3 1600 9-9-9-24 @ 1.5v Model F3-12800CL9D-8GBXL http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Since 'I' have an affinity towards CAS 8:
G.SKILL Ripjaws X Series 8GB (2 x 4GB) DDR3 1600 8-8-8-24 @ 1.5v Model F3-12800CL8D-8GBXM http://www.newegg.com/Product/Product.aspx?Item=N82E168...

edit: Ripjaws X are fine for single sets, but not so great if you want 16GB. In that case go with Corsair Vengeance.
CORSAIR Vengeance 16GB (4 x 4GB) DDR3 1600 9-9-9-24 @ 1.5v Model CMZ16GX3M4A1600C9B http://www.newegg.com/Product/Product.aspx?Item=N82E168...

They do have several 16GB Ripjaws X kits with different timings as well. I have 12GB of Ripjaws X in my P67 system (one 2x4GB kit and one 2x2GB kit), so multiple dual-channel kits do actually work together. Some people just get unlucky with a bad stick.

Good advice from all^

Your real application performance or FPS may improve by as much as 1% with faster ram. Not much worth it to me.
Synthetic benchmarks will look great, but are irrelevant.

I vote for 12gb, but really a 8gb kit is great. There are no games that I know of that are written to take advantage of more that the 2 or 3gb that a 32 bit os allows.

Until a few days ago I would have agreed about the Ripjaws X, but there have been too many problems with 2 kits of F3-12800CL9D-8GBXL edit: to be clear the problem is running them at 1600 MHz, 1333 MHz was okay, and has nothing to do with Memtest failing. It's weird, Google those kits.

I totally agree about any advantages of >8GB for games - none as long as you 'shared video memory' is maxed-out.