I never use 6.5" pads unless its an Airplane or a big tall, flat Van..
The smaller backing plate and pads 1" smaller in diameter can get into more places than the larger pads..
And I have a spacer on the end of the Rotary as well, to further get closer without having the machine in the way..
You just have to be careful about the spinning spacer and make darn sure you do not touch anything with it, or you will be buying it..
The only people I see using the bigger pads are the guys in the automotive body shops, and they are usually wool, and very dirty...
Why do they use them ? They can cover a lot of area really fast, the new paint can take the abuse because its never been compounded before, and of yeah, the Swirls are On-the-House !!! Bonus !!! Score !!!
Well... I shouldn't be so hard on them - I used to work at a few shops too...
But, I never swirled anything because I was taught how to not swirl, and I really like perfectly clear, no defect paintwork..
I have watched people on Automotive Assembly Lines using air powered rotary machines and they never use big pads.. Just too much surface area to look after and it cant get into every spot like a smaller footprint can..
Any size pad can work though, you just have to adapt to it and make it happen !
Dan F