I have a G20 and did have a G29. The G29 has too short of a barrel to get any potential out of the 10mm. I could not find a reload combo that could get the G29 up to 10mm spec. You would be better off getting smaller G27 with more rounds. The 10mm needs a longer barrel.
This may be your experience, but it's not the reality that I have easily
and routinely accomplished. And I don't mean to be flippant by using those terms -- I'm simply trying to express that I've returned fine numbers without going great gonzo with over-max, ball-bustin', brass-killing loads. I have not had to get crazy with dangerous handloads to return very encouraging chrono numbers with handloads.
Using 180gr FMJ slugs, I return a 10-shot average of 1,057 FPS with a handload that is WELL under published max and fun to shoot, using Alliant Power Pistol. I've shot thousands of these. I have room to advance this load in search of more speed, but I simply haven't bothered.
More 180gr FMJ pushed by a very mid-range charge of Longshot repeatedly gives me 1,136 FPS average. That's a middle of the road load.
When I push the Longshot up near (but STILL under) published max, I return 1,209 FPS all day long. That's an average velocity, not a "one shot peak on a 105 degree day."
Easily available factory Winchester Silvertip load out of my Glock 29 returns an average just over 1,100 FPS. That's a 175-grain slug.
And my current carry load is the Buffalo Bore 180 grain JHP and it returns real-world chrono verified numbers
of 1,259 FPS
with a 180 grain slug. That's 633 ft-lbs of energy. It's expensive ammo, but it runs.
of the above quoted real-world chrono numbers are from loads out of my own personal every-day-carry gun, an MML-prefix Glock 29.