Kevin Insco here. Dont know if you remember me, but we grabbed a few drinks w/ Shannon and Derek at the hotel lounge at Tulsa.
Probably the best minor load out of the MP9 is going to be basically what Bryan suggested. 147gr bullets, 3.4 grs of Titegroup or N320 (they feel almost identical), loaded to somewhere 1.140-1.100 OAL and either Winchester or Federal small pistol primers.
Now, out of my CZ SP01's, they like the ammo at 1.100 OAL, but you can prob get about 1.140 out of the MP, but I have not tested that. You might even get them longer, but I dont see any reason for benefit to go longer. Thats the softest, prob most accurate load. That should be about 129-130pf.
If you like 124's and want to stick with them, out of my SP01, I got 124gr, 4.1grs Titegroup, 1.110 OAL and Fed primers and it gets 129-131 pf. Not bad load, a little quicker sight return, but faster slide action.
My PD is switching to the MP this week and Im doing the transition w/ our full time training guys. MP appear to be nice guns, I like them alot, but its hard for me to get away from my CZ's for USPSA.