I was 6 boxing eq 1 and now started 5 box wow on a core i7 965 extreme 3.2 ghz (not overclocked)
memory : 12 go ram 1333mhz triple channel - graphic : asus gtx 285 top 1go
for disk speed i took 2 raptors 300 go 10000rpm and put them in striping.
screen is a full hd samsung 40' tv and case is silverstone raven for silence.

I have yet to see any lag, i think it could easily run a few more sessions.