In general the answer might be no as most people arent using 64 bit OS so more then 4 isnt in the script
But Ive found over 4 can easily be used and therefore useful if you include all the extras that go with a new game.
So the biggest one is texture memory, this is main memory used where the graphics card overflows.
Then theres the OS, in theory you can swap out unused programs to the pagefile and its not a problem but to do that every time you load the game or even alt tab is a pain and laggy till it completes
I used to play bf2 with 512meg so the above is possible but its horrible, avoid the pagefile always if you can
Then there is teamspeak mumble fraps or other gaming programs. More then 4 is going to be useful right now (and you need the 64bit os obviously) but not essential
Finally I find windows tries to cache everything, really saps spare memory. If you have nothing spare or free mem is low - your chances of it churning away juggling programs increases, which you means you wait and/or lag.
You can get lucky like my bf2 example but windows typically is a pain to use on the edge, space to breath is best
I say this as someone who went from 2 to 4 to 6 now since Xmas. Ive switched from ddr2-5300 to 8500 then ddr3-12800 Those numbers relate to peak transfer rate in MB apparently
So Ive more then doubled the memory speed and I'd still say its all about the hard disk mostly (get SSD).
Thats way more noticeable then memory everyday especially if you are using the pagefile at all.
So in order of noticeable gains, its how much not how fast.
Speed up the hard disk, dont use the page file by always having enough memory space and then finally worry about your memorys bandwidth and all that benchmarking stuff.
http://www.thebuzzmedia.com/ddr2-800-vs-ddr3-1333-does-speed-matter/
I put a SSD onto a 7 year old build, 200mhz DDR1 and its a great improvement
