I currently use tp, ten, alto, bone and 3 rhythm in Finale with playback on a PB G4 867 MHz and 768 MB Ram. If i don't use the reverb settings too much i have pretty good playback without stuttering, and my computer is WAY under the requirements for JABB. So...with your setup you should be fine. I understand that if you plan on using a full big band you REALLY do need the G5 and a lot of ram(2 gig minimum). I plan to go to the new macbook pro when KONTAKT is compatible under the Intel chip.