3 Boxing WoW: Use 1 computer vs 2 computers?

I used to 3 box WOW on 2 computers, but took a break for over a year. At this point I am down to one older computer.

I was looking to either build a new computer with the 2500k sandy bridge processor and use it to 3 box by itself, or I would use my old computer to run the 2 slave accounts while I run the main account on the new computer.

My old computer is getting tired and I would probably either upgrade it or just build a budget 2nd computer if using 2 computers was "better".

What are the pros and cons of 3 boxing WoW on 1 computer vs 2 computers?

If you want to record videos and/or watch movies/TV and/or surf the web and all that, I would probably run the two slaves on the alt PC. THen again, if your new Sandy Bridge PC is a quad core or higher, you can run all 3 and do just about anything else on it at the same time mostly likely.