The V3 internals are the same as the V2 (even states this on the Griots webpage)--the only changes are ergonomic which seem to be appreciated by those who have used it. I think you will find that most feel the GG has considerably more power than the PC--especially the earlier PCs. Of course the lifetime warranty is still in place which IMO is a huge advantage.
I've only tried Machine Polish 3 and found it to be very mild so it is religated to polishing our Corian counter tops. If you're looking for great polishes consider HD Cut, Polish and UNO.