Has anyone here played an AS&SH game with characters 9th level or above? How did it go in relation to doing that with 1e Ad&d?

Side question - how much experience do you have with playing 1e or B/X or similar ruleset at these high levels?
Do you feel the game breaks down in some ways? Or do/did you enjoy it?

Thanks, just want to hear some opinions. I am running a level 10-12 1e game this wknd...