I like the 40, and have been thinking about buying one, but haven't justified it yet since I already have a 6" long slide 10mm on a gen3 SF frame. Wish they offered the 40 in a standard slide without the MOS cut though.
Just a side note, maybe you already know, but in that 6" barrel you can push 180's considerably faster than 1250 if you want to, either with Underwood ammo or handloads. In my longslide I'm mostly shooting 200's at 1325; those do 1250 in a stock G20 barrel.
