I bet your not that far off!! I have seen some chrono. Numbers for 6" barreled dillons and they are pushing 2000 with 124g bullets.
BUT, it's just a number really, unless your just wanting flat tredjectories for paper shooting that is cause the single bullet that will hold up the that velocity is a FMJ... The 9mm barely gets a 147 going over 1K so nearly tripping the velocity will have quite a effect on expansion.
FMJ isn't first choice for shooting game. The 9x25 is a velocity hound. The difference in velocities when longer barrels are considered, are pressures the calibers run at. Most handguns are lo pressured, not so with the 10MM and it's offspring the 9x25. They are right at 40K like the Maxi! The vel jump in longer barrels is head and shoulders about a 15-20K 38 spl loading.
I can see the allure of a 9mm/40/10MM/45 in a Handi, but it's just not my cup of tea.
Now if you Make it in a semi auto that utalizes the same magazine as its hand gun counterpart and you have my attention and likley my $$ too.
CW