Four Horsemen - pretty good 14 G1s at 1m. In breeding barn, sire of 3 G1 winning horses
Frankel - good at 2, poor at 3.
Special Forces - very good, 7 G1s at 1m-1m4f, 2nd season sire, already has 3 G1 winning horses
Minnesota - good, 6 G1s at 1m-1m1f. Breeding barn, 1st foal a 2yo Group winner
Zeus - dreadful
Gunga Din - very good, current best 1m1f horse on dirt
Bayonetta - similar ability to Rippersnapper in the league. Multiple G1 winner at 1m4f
Underground Resistence - bad
Okemo - awful
I think the older they get the worse the produce but you get 6 or 7 good years.