In a 64-bit system with a powerful graphics card, 8 GB of RAM really is a must if you're going to play demanding games. This is the case regardless of whether you're using 32-bit or 64-bit applications. However, even more than 8 GB of RAM can be subjectively noticed while playing. There is no real need for 16 GB of RAM, though. Going with 8 GB is quite enough unless you're running some taxing application in the background. We’ll comment more on this subject later, because the problem is often overestimated, as shown in our 64-bit gaming benchmarks.
As other's have posted RAM is cheap now and for $15-$20. you might as well get it. It will not make a significant diff in system performance or games but it does allow you to open more apps concurrently or use large programs, do video editing, etc.
Don't mix RAM however, just get ONE matched, tested RAM kit approved for your CPU.
i am using my computer especially for gaming nothing more demanding than games...
If you plan to use your computer for more than 3 years, 8gb or ram may be more useful in two years or so. I make this assumption based on the fact that when i bought my computer in late 2008 2gb or ram was said to be the 'sweet spot' or more than enough for gaming and I decided not to pay $30 back then to get 4gb less than a year ram prices were alot higher and to this day I somewhat regret not getting 4gb and we all know a while now 4gb is well utilized in several games. I think game size increases, texture quality improvements and the potential use of a higher mainstream resolution than 1080p would result more memory would be need. That being said this is only my speculation and industry forecasting, 4gb should be enough for a while but for as little as $15-20 to improve the gaming potential of your pc for the future I would say get the 8gb!