Why not make Stamina like Free Throw % used to be? The FSS could still apply on how fast they gain points but there is no cap, just like IQ. I think this could be balanced with a system that makes you have more stamina on your team in order to run both uptempo anything and press.

There could also be a soft cap by their position. PG/SG would be like 92-95, SF would be 87-92, PF would be 84-88, and C would be 80-85 for soft caps. This would also make it a little more realistic because anyone can be trained over time to have more endurance on the floor if you really push them but usually bigger guys do get tired faster than quick little guys no matter how much they train because of the size difference in bodies and the "work around the basket" they do.

One other thing is that if you find this not to be realistic then look at the IQs your team has and the players GPA, more than likely the 2.15 guy is not going to have A+ or even A/A- in anything because he is "slower". So if you really want to go for realistic then personally I believe that players should have Max IQ Ratings in each Off/Def as well. Then having a player with A+ M2M skills would really set him apart as a shut-down defender.