Quartus II is just a software program. You can run it on any machine provided it uses one of the supported operating systems and has sufficient memory.
As far as a comparison. Obviously the more processing power you have, the faster the software will perform. You will notice a huge difference in compile times by using a multi-processor/multi-core machine versus a single core.
Presently my machine houses a Intel Core 2 Duo E6850 and performs quite well. I've also run Quartus on a dual-processor AMD Opteron machine which performed comparably to the Core 2 Duo. For a short time I ran on a single 3.0GHz Pentium D in which compile times were about 3 times longer then the other two machines.
Jake