I think that the problem with the 6.5" pads being too big only applied in the old PC7424 and maybe the PC7424XP. If you have a GG6 or a G110v2, you shouldn't have a problem because those 2 machines have a very powerful and capable motor. I don't think I would have a problem using the 6.5" with those machines if I didn't have a choice.
Another problem is that the height of the 6.5" inches is a lot higher than the 5.5" pads. The increased volume of the pad requires the machine more power to move the pad. From this thread (
http://www.autogeekonline.net/forum/how-articles/27166-how-maximize-your-da-polisher.html), the 5.5" LC flat pads measure 7/8" high. I think the 6.5" LC flat pads would measure 1 1/4" high (not in that thread).
Per that argument, you would think that the 7" Softbuff 2.0 pads from Meguiar's would even require more power than the 6.5" LC pads based solely on the pad diameter. But IMO, this is a flawed argument. When you look at the Softbuff 2.0 pads, the center of the pad is recessed to allow the W68DA backing plate to self-center. Only the outer 0.5" of the pad has full height. Everything else has half (approximately) the thickness of the foam pad. This IMO has less the volume of the 6.5" pad therefore making it easier to move and rotate from the DA.
I've done a lot of correction using the W8207 Softbuff 2.0 polishing pad with either M105, Ultimate Compound or M205 without any problems. If the DA wasn't rotating the pad enough then I wouldn't be achieving the results I've been getting when I used them with my G110v2.
Just my $0.02.