I go to UT Dallas, so we follow the UT system of grading.
If high 80s is an A-, which is 3.67. Then anything 90 and above is an A/A+ (4.0)? Then there is no point in aiming for anything higher than 90.
As for exceptions, you might be right, but you never know if you don't try. I mean if you end up at say 92.3, borderline between an A- and an A, wouldn't you want to try and see if its possible to get it bumped a little? If it works out you'll end up having an A, if not, you still get an A-. Might as well give it a shot.