2 consoles and one window. The Xeons are hyperthreaded to make 4 logical processors. I still have 25% idle time. It may be somewhat impacted, but not enough to discount another process.
OK... just curious. However, I'll mention that the FAQ advises that running the GUI version with others might cause some instability; there's also a bit about trying to treat HT processors as duals. From what I've seen, they recommend that you don't try to keep each HT busy, just use a process for each physical (or true) CPU you have. If I can dig up the URLs I'll post them.