I just recently started looking at the 10mm and you hit exactly on what I liked about it. the bullet weight range it can handle and the pretty large speed variance that comes with that. I am not aware of another pistol caliber that is quite that diverse. I already had the dies as I had a .40 cal set, and I already had .40 projectiles laying around.The G20 10mm was offered before their .40S&W. Even before Glock had a .45. It was built from the ground up to handle the full powered 10mm loads and is responsible for keeping 10mm around because when .40 came out 10mm was in major decline. A few of us hobbyists kept the 10mm alive because it is a reloader’s round dream, and can be used for hunting most medium sized game in an autoloader. The resurgence it’s seen in the last decade is a result of that and after the 96 sunset meant that many of the other major manufacturers felt free to start making full size guns again.
The G20 chamber is perfectly fine across all generations for full power factory loads. The earlier ones were looser and many of us switched to aftermarket barrels to ramp up the power or to shoot lead as the octagonal rifling is more prone to leading, but that is not indicative of a design defect, it was never intended from the factory for either. I own every generation of G20 and G29 as well as most of the non-custom manufacturers offerings (still looking for the BrenTen for my collection). In spite of the dismissive label of “Glock fanboy” casually tossed around by some to try to avoid actually acknowledging valid points, my real fanboy passion is the 10mm.