I still feel well with my LGA1366 and 12GB installed three years ago. I assume that one should wait and get the newest LGA2011 (with DDR4, which is not released yet) with a six- or eight-core CPU and memory modules set in quadruples if he has money.
I used to play both PVP and PVE with Pentium 4 Prescott, single-core, 3GHz, 3GB back in 2009 (December) - 2010 (September).