You should get a Quad. Games are starting to make real use of the extra cores these days. I believe the time when you could get away gaming with a dual or even tri core is just about over.
Personally I went with a Dual 555 BE about a year ago and am now thinking I really need to upgrade to a decent Quad, my 555 BE can over clock and unlock to a tri core but I don't bother. I can play games ok but notice the differrance when I do unlock, mainly did it to see if i could and to bench it.
Mactronix
