Oblivion will be a thing of wonder, you'll love it. Crysis is a real GPU hog, you will have enuff GPU/CPU to do Crysis well, not 100% on everything.
Oblivion will be awesome, and try Mass Effect after Oblivion.
Get an aftermarket HS for the GPU/CPU and overclock both too, about $120 more for high quality HS. Thermalright is what I recommend, and have used. The TRUE for the CPU and the HR03 for the GPU. Very quiet too.
Ohh yea, a case...... the Antec 900 is a popular air cooling case, just a suggestion.
Read up at xtreme forums and OC forums in the Air cooled area for some real OC insight.