Cats have some of the same evolutionary features as other mammals well-adapted to the heat, such as large ears and long tails, proportionately longer limbs, higher body temperatures and rapid heartbeats, and alot of sleeping... as opposed to squatter, more centralized body structure, small ears, short limbs, lower body temp and slower heart/respiratory rates, etc.
Except the ones Kai Bengals mentioned, which should be kept much cooler--but to me its the same as human ethnicity, for instance my ancestors are from Wales and Scandinavia... so clearly I don't do very well in hot weather and have very pale skin and my family has lower normal body temps than average, usually around 97 F. I'm willing to bet that Zissou feels better than I do in the heat, regardless of fur, since sometimes when I'm boiling she sits in the sunniest window she can find.
That said it's pretty obvious when your otherwise-healthy cat is overheating, such as seeking out shade, sprawling out, drinking more water than usual, etc. And if they start panting they need to be treated for the equivalent of human heat exhaustion...
I still don't see anything wrong with giving your cat's fur a TRIM with a guard, such as on a beard trimmer, on the areas not a head or feet, but I wouldn't shave it with a safety razor or anything. Yes, I realize that cats don't sweat, but you have to be kidding if you say that they won't lose any heat this way. We lose heat through our skin in the winter... but we don't sweat it off!