Loren's thoughtful comments made me realize that I should have added in my own earlier posting to this thread that I base my 35x-per-inch-of-aperture rule on planetary observing. When observing the Moon and Sun, I rarely go larger than full-disk observing, so I never really explore the limits of magnification on those objects. Planetary observing, however, is another animal altogether. It's that area that I find myself exploring the limits on how much magnification I can throw at Jupiter and Saturn in particular. There, too, I should also add that, since these planets have been at low altitude in recent years, it's all the more challenging to get crisp high-power views. Especially as Jupiter rebounds to higher altitudes in, say, three or five years, I'll be keen to re-evaluate my 35x-per-inch-of-aperture rule.
One advantage a scope the size of a 3.5" Questar has over, say, my C8 is that the smaller scope has to look through a narrower column of atmosphere out into space and is thus less prone to the effects of bad seeing. Lately, I've gotten surprisingly sharp but significantly dimmer views of Saturn in my Synta-built 4" Mak and Orion Edge-On 9mm eyepiece (144x). Most often, I use either a 14.5 or 12.5mm Edge-On eyepiece with my C8 for planetary observing (140x and 163x, respectively). The view is much brighter in the C8, but I find I rarely use my 9mm eyepiece (225x) in that larger scope simply because the seeing just doesn't permit it most often.
I will also admit that my '62 Questar has failed coatings, so any high-powered views in that scope are compromised. This discussion is all the more fuel on the fire in terms of me wanting to restore the optics on my Q. Still, my expectations about what that little scope can do are tempered by simple virtue of its small aperture. But who knows? After I get my optics fixed up, maybe those expectations will be confounded just like my initial expectations with what my Q can do even its current state were (see this recent post of mine).