I am not positive, but I would guess that the server would run best on less cores. It may only use one at a time, so having the fastest speed per CPU would probably be better than having more CPUs with a higher total speed if you know what I mean.
So, a AMD 6400+ X2 that runs 2 cores at 3200 would probably be better than a Quad Core 8000+ that ran each core at 2000 (just made the second CPU stats up).
I run my server on a single core 3700+ atm and it handles well. But, unless you are expecting to have hundreds of players on your server, any new CPU should work just fine. The most important part is RAM and with 4GBs, you should have nothing to worry about
Threaded Mode
