since the engine change the top single season player improvements I've had were 104 and 91.
Both had 90+ WE and 8+ high potentials. In addition, they both also picked up 20+ during that first offseason.
As for a team that can be a bit skewed based on the number of upperclassmen vs. lowerclassman. I should pick up 60+ on a fairly well balanced team this season.