It's rarely this hard to give a clear assessment. The facets of various memory issues are too extensive and vary widely depending on each user and his or her relevant applications. Interestingly, certain 32-bit programs in 32-bit environments with 4 GB of RAM installed will benefit more from going to 8 GB (or higher) than some 64-bit applications in 64-bit environments. As a side benefit, this approach closes the annoying gap between the 4 GB of installed RAM and the 3.25 GB usable by 32-bit Windows.
We tried to illustrate years ago why not all performance improvements can be shown simply in terms of frames per second. This is why our conclusion departs slightly from what you might expect only from looking at graphs. We based this conclusion on our objective measurements with subjective impressions included, just as we highlighted the benefits of a RAM disk for temporary files.
Conclusion and Recommendation
Based on our measurements and impressions (and taking falling prices into account), we thoroughly recommend a minimum RAM size of 8 GB. Using 12 or 16 GB only makes sense if you're planning on using 4 GB of more of this higher amount as a RAM disk, helping accelerate the reading and writing of temporary files. This applies equally to file compression, video encoding, and heavy image editing.
Other than this, you might want more RAM so the graphics card can allocate more system memory for its own use. We saw this pay dividends in GTA IV, for example. You won't see an overwhelming performance increase unless you're using very memory-hungry programs, but you will get a system with enough RAM for the foreseeable future.
Given our observations and low prices on memory upgrades, this is the time to hunt down a high-capacity memory kit for your system. In the end, it’s never wrong to make a step knowing that it will improve performance and provide some reserves.