I used 4 gig forever on my 32 bit win 7 and now I've gone 64 with 8 gig and a 1090t and it seems about the same when just doing the net and normal type things, haven't really been able to do much gaming with the new setup yet but 8 gig seems fine.
Finally got a PSU that can handle my new to me 4870x2 so maybe I'll finally be able to stress it out a bit when I get Crysis 2 and maybe redo some of my Stalker Call of Pripyat.
My old Nspire 750 Xtreme, that is the OEM of the Thermatake tough power 750, would shut down every time a game loaded unless I slowed it way down or disabled the second core. Got a new Thermaltake Black widow 850 with a big single rail for 12 volts and no more issues.
Of course I think more memory is always better, just like a faster multi core CPU is better but ya got to live within your budget just like I did when we slammed this new rig together so you should be fine and can always upgrade to more when a smokin deal comes around.