There isn't much right now but i5 is a deadend in term of future upgradeability since most of the newer CPU coming out next year will be on the 1366 (i7) platform again.

Your choices looks good but SSD is a must for 5 boxing imo, There's something to be said for hearthing 5 characters into dalaran at the same exact time and load under 1 second

You might want to also consider a second graphics card to handle the 4 on the other monitor

My rig is I7 920 @ 4.0ghz, 12gb of ram , 2x285gtx and 2 intel x-25m in raid 0.