2.66 quad, 8 gig ram, Geforce 8800 GT 512 mb, Windows Vista 64, I typically run all 5 clients at 1600x1080 roughly..sometimes i'll chop the rez a bit so i can cascade the clients over both monitors but thats what im running fine without issues, using 2 24" monitors, It's kind of a pain that you can't shrink the windows smaller then 1024x768 like you could in wow, just drag the corner of the client and resize..but oh well. I don't find eve with max settings that hardware dependant..mind you I think my box has a bit of free horsepower, but still I've never yet ran into an issue where it was lagging bad, not like in WOW with 5 clients open.

I've never been to jita yet with my 5 accounts though so I can't say what it's really like to be in a super packed system, but in a normal area 50-100 ppl i dont notice any lag.