Building new system, changing back from an iMac. Last PC I built 2GB pc3200 was real High-End Seeing that the pricing is totally changed, 16GB purchase is very affordable... but is 12GB and over just overkill and added heat?
If you're building a dual-channel system, I'd get 16GB and call it a day. This way you can run without system cache and still have 30 tabs + torrents + whatever open while you're playing games.
At this point I have 6GB and Crysis 2 DX11 + high-res texture pack is crashing while loading a large map (basically any map other than the very first one). Crysis 2 DX9 worked fine though. Crytek recommends 8GB for the DX11 version.
I also occasionally get system out of memory errors if I run Dragon Age II at the same time as a few tabs in Chrome.
I couldn't find an extra 6GB kit of my RAM, so I ordered a 12GB one today. I don't think I'll be RAM blocked anymore.