I bought a player with tremendous JS and tremendous JR. He's a mediocre shooter from inside the arch, but he can torch from the 3 pt line when he decides to stretch it out (which isn't nearly enough). One thing I've noticed is that he randomly pops up and takes 40 foot jumpers with regularity with time on the clock. No one else on my team will do this. I don't know if these things are indicative of the players extra jump range or not, but I'd recommend not going overboard with jump range. Definitely keep jump shot a ways higher in comparison.
I should also note that he's performing this way against 95% bot opponents which I can only hope have awful defenders. It's perplexing to me, but from what I conclude based on everyone's opinion on jump range coupled with my new found players results, it probably isn't worth it to train past prominent unless your jump range is significantly higher maybe.