Glock 40, 6" 10mm with my 165grn handloads.
I invented the Glock 10mm longslide in 2004 using a German G21 .45acp 6" slide. The 6" 45 acp barrel came from Jarvis and it balanced out really well, however, later in 2004 I decided that I wanted to see if I could convert it to also shoot 10mm.
I talked Kevin of KKM Precision into making me a 45 10mm conversion barrel for it. With a .45 LCI extractor, 10mm mags and Kevin's conversion barrel, I had the parts to assemble the world's first G20/21L. It's shown below the G21 version in the picture below.
With the 10mm barrel, my hottest 165grn handloads chrono at a blistering 1,589fps with 925ft/lbs of ME!!
Glock finally developed the G40 a few years ago but I can tell you from over 9,000rds of hot 10mm, the 6" 10mm is a powerful pistol. I went on to tweak it for USPSA limited shooting and then as just a fun shooter.
Currently, it looks like this with a hard chromed slide and mag well.