[koohead]

Don't believe there is a simple way to do this. If you are using star ratings you could go by those to determine who your best pitchers are and who the best players at each position is. The Position Strength report will identify the best player at each positon (I'm assuming according to SISA) so in that sense you'll know when a minor league player has grown past someone in the majors.
Oh, you can use the Minor League report to get a quick snapshop (again, in the opinion of some mythical scout) who is ready to move up to the next level or even the majors. this is similar to the minors report from 6.5. If it says someone is ready for the majors, the at least you can use that as a starting point to compare that player with everyone else at the position you currently have in the majors.

Short of that, I think that's the fun of OOTP...you have to take the time and study all your players and decide when someone is "ready" so to speak.