Jesstzn-I've never noticed any big diff when using different size plates on my Griot's, but then I don't bother to change the weight on my PC either (I just use the 6" weight with everything). OK, there's a bit of a difference when using 3-4" pads, but it's no big deal IMO and I'm a bit sensitive to polisher vibration.
Note that the whole "which weight" thing for the PC is based on a backing plate spinning a single sheet of sandpaper; the only diff being the different weights of the two plate sizes (as opposed to the weight diff of both the plate and the pad, which is often wet with product). With the different backing plates (and some weigh a lot more/less than others, even in the same sizes) and al lthe different pads, and the differing amount of product that's on the pad (compare KBM compounding with sealant application), well...the whole idea of auto detailing with a PC is just totally different from what the machine and it's plate/weight systems was designed to do.
