You could do 6-7 pretty well. As I understand you are using one hard drive. Having Windows on the same drive as your apps, especially games, can slow your gameplay down. A cheap solution is two small, fast drives in a RAID0 array. RAID0 offers no data protection but some speed benefits. Just having one separate, 7200 RPM, drive will make it bit better. I have a similar system with 1 9800GT and 12GB of RAM and I run 10 decently well. I prefer to split the load over two systems still (2 x 5).