You have to bear in mind that there are two parts to Ship Simulator. While Ship Sim can see two processors (don't know about quad, though), Questviewer apparently can only see one.
Now, Ship Simulator needs 2.4 GHz (single processor) or 2.0 GHz (Dual). But Questviewer only sees one processor, irrespective. However, my understanding is that it doesn't need 2.4GHz. (It's difficult getting to the figures for this, so this may not be correct. It's my best guess, having looked at 3DQuest technical data and so on).
Best option is a single processor 152GHz with 18TB of RAM. Or as close as you can get.
Ultimately, despite the hype multiple processors are not properly implemented (if at all) by most software packages. Windows itself is less than good and lots of the core functions within the Windows Kernel don't see multiple processors. So all in all, the extra speed is largely an illusion (or marketing deception, the choice is yours)
I must go and lay down now. My brain hurts.