I run my 5 box team on the following

Intel Core 2 Duo E6600 / 2.4 GHz
2gb ram
7950GT card

1024x768 with 30 fps for main on screen 1
the four on follow split a 19" 1280x1024 screen and is set to lowest in all and 15 fps
Keyclone and Maximizer is a must for me

I dont have much of problems. Either in instances or grinding quests. Only thing is when I travel by bird. The swift graphics change means heavy loading on the 5 accounts. My solution is quite simple. Send the 5 man team off to their destination and go afk a few minutes. By the time I am back all 5 have loaded proper and I am off my merry way. ^^

I know some would /cry over 30fps/15fps but since I am only into PvE is good for me. No need for more atm.