all the benching on guru3d is done with a 5960.
i have yet to see a gpu test, where its not significantly faster than what i expected (vs my 3770k).
it does get lesser the higher the res (your playing at), but i dont game above 1440 so i would still gain a bit.
almost all new games do run on more cores.
BF is actually using 8.
since we still have the OS/AV and other stuff, i dont see a reason not to go with more than 8C if you have the cash for it.
do recommend to wait for the 8C/16T reviews of ryzen which beats intels 6900 while at least 500$ cheaper.
i know i'll get a 8 or 6C amd instead of the 5820, but mainly because of price and a "future proof" socket (AM4),
so i dont have a problem upgrading in 2y.