Using Garry's method (if you can call it that...and who cares anyway) I can't see where GSM rating would be that important considering the towels are soaking wet with a slick wash solution, even when using ONR I can't see a problem.
I think super plush towels are awesome, but they also tend to make people feel warm and fuzzy inside when they use them, not sure how they feel when they pay for them. I know for a fact that Garry has used many a towel from a certain large store chain without concern. His words, not mine, but that was 5-6 years ago and he may have changed. Of course becoming a salesman has a tendancy to change ones thoughts as well. Garry is a great guy and I'm sure would answer your call and questions concerning this issues and give you up-to-date input from the man himself.
In my mind I'm wiping off a wax or sealant both of which provide lubrication, even the dust from a wax. If I use spray waxes, detailers, rinseless washes, or soap, then I'm still covered. Waterless may be different altogether, then again if I spray waterless solutions on my paint I also pre-wet the towels. I'm also of the same mind-set as others that at some point with waterless you will scratch the paint. It's not if, it's when. I still like to pressure wash the grit off first, but if you do that it sort of defeats the purpose, so then you have to figure out how much dirt is too much dirt to do a waterless or rinseless. Lots of discussion and varying opinions on this subject.
I never wipe dry...and I think that is key. Even when drying after a conventional soap wash, if I use towels instead of air, I always pre-wet those towels too and then wring them out before wiping to dry the surface of the paint. Even with high GSM towels that are softer I still will dampen them. Old habits die hard. Water itself is a lubricant.
That's my thoughts, but keep in mind I'm no professional. Other's mileage may vary.
