Hi, I'm looking to make the switch from PC to Mac. Buying a new PB is out of my budget, but am looking to buy second hand. Is there a huge speed difference between the older 1Ghz PB, 1.2Ghz PB and the new 1.67 PB, or do other factors such as Ram have a greater role? Can't seem to find any benchmarks anywhere directly comparing them.. Cheers for the help!