I've used the search function for player IQ development and am only finding stuff back from 2009-2010. Also looked in the HD guide.
I'm sure it has been discussed before, so if someone can direct me to the thread or post I'd greatly appreciate it.

Just looking for a few notes on:
if players can max out (aka not improve anymore)
what's the usual practice minute / work ethic combination that is most efficient.

thanks!

I'm not sure I can answer your exact questions but here are some thoughts

1. I dont think players ever max out in IQ - any player can get to A+ for sure - and I think even at A+ there is still some tiny progress
2. Players improve more slowly as their IQ improves - there are threads on this
3. Most folks say that they allocate apx 20 mins of practice to each of their offense and defense. If your players dont have much potential to improve - or much remaining potential - you may want to nudge that up to 25 each. May also want to nudge up to 25 each in some other circumstances.
4. More work ethic is good and will grow IQ faster. If you look at teams, you will see that some coaches care a ton about work ethic, some less. Below a WE of apx 15, improvements in skillz get darn slow. There are threads on this.

The improvement function is f(WE * HSGPA * practice). HSGPA cannot be improved (except that it changes when a player goes JuCo). WE improves with starts & minutes.

The letter grades correspond to a background number that is hidden. Not sure what form that takes, but it may not be clear whether the letter grades have elongated gaps while the raw number behind moves linearly. Confident there are different "B+", for instance. Fairly confident that there are different "A+". No idea how much the latter matters.