Sorry, I didn't see your question until this morning. Yes, my G20L has a longer slide and barrel, however, it's not at all bulky. Consider that my Glock G20 with 17+1 rds of 180grn hot 10mm hardcast handloads on board is more compact and actually lighter than a comparably performing 6" barreled .357mag S&W 686 with only ⅓ the ammo load on board.It's an interesting idea, but the 20 is already pretty bulky. Do they even make a holster for the G40?
I wouldn't want a 10mm if I didn't handload. It's sad to see how weak most store ammo is. I get 1250 fps out of a Glock 29, which is not too bad.
As to holsters, it fits just fine in both my leather open nose Don Hume Paddle Holster made for a G20 that I use as my range holster as well as my leather Yaki Slide holster I use for 'woods walking' to keep it tight to my body.
BTW, my 'nuclear' 165grn handloads chrono at 1,589fps out of my G20L at my range at 6,100ft asl on an 84° day. That's 925ft/lbs of ME and with the longer sight radius it gives me the ability to 'plink' steel plates at 200yds.