Since I've moved it to where it isn't looking through trees, my 90CM primestar does a nice job on AMC21. I get all the channels people talk about, including the DVB-S2 from La (except when it's raining heavily), and I get a lock on the IP/DVB transponder when it's up, 12 transponders lock fine {actually 13 including one strange one that gave signal lock but not data lock}. My 90CM Fortec doesn't do quite as good a job (8 of the 12 transponders), but it is really a bit smaller than 90CM (ie the advertised size is really an exaggeration), however it is looking through tree limbs, and not quite all the leaves are gone yet (oak leaves are still hanging on a bit). The Fortec gets the main transponders fine (140, 180, 150, etc, but not the DVB-S2, and a couple of the weaker DVB-S transponders. But I expect some of the missing transponders to come back in a week or so when the oak leaves finally are gone completely. A month ago, the Fortec didn't get ANY channels on 125.
So anyway, I don't think you need a 1M on 125. A good 90CM will get all the channels discussed here, and even a fair 90CM will get most of them.