i'm thinking of buying a 2008 mac pro second hand, and i wanted to know known faults etc. so i know what to watch out for when buying one.
thanks in advance
Yes, it was a big performance leap from Mac Pro 3,1 to 4,1. And yes, 4,1 use DDR3 RAM. But SATA 2 on internal bays, not SATA 3. You can see all information with the MacTracker application.
why a 4 core 4.1 over an 8 core 3.1? are they faster?
No, they are NOT faster (at least not at everything). In fact, for tasks using all 8 cores (handbrake, etc.), an 8 core 3,1 will destroy a 4 core 4,1. (A faster-clocked 4 core 4,1, if they made them, may be marginally faster than a 3,1 in every-day single-threaded tasks.)