I remember when getting my hands on a 3.2 P4 would have been brilliant. Sadly, compared to the newer stuff these days, it's a small step up from wasting electricity. Work out how much you'd spend on electricity per month running the P4 and donate it to charity. That's what I'd do.
However, in answer to your question, I would run two standard clients on the P4.
edit - scrap the two, just run the one and disable hyperthreading. Uses much less power for tiny performance hit.