I don't know too much about hardware and stuff :-). Currently I'm dualboxing RK/Hunter on one laptop, both clients run a little bit slower then they would if they ran on 1 pc.

I'm not sure if you can run 5 lotro clients good enough on 1 killer pc though, it takes a lot of memory.
Make sure to get a 64bit OS to make use of your ram. I think 6 or 8 gb ram will help you a bit more running those 5 instances at a time.