Ummm...
Things have changed, as they often do.
Nobody using any sane (published) load data is getting more speed with Longshot than they are with #9, and if they think they are I'd bet good money their chrono is lying to them.
I've shot nothing but 200 grain XTP's in my 10 with Longshot, #9, Power Pistol, and Unique....None of them get anywhere near #9 for both speed and consistency...single digit extreme spreads and 1,305 fps from a 7" barrel using 12.6 grains of #9, not even a max load, Hornady says 13.2 is max...I've shot that max load at nearly 1,400 fps from the 7" barrel....and VERY loud.
Max load of Longshot (8.2 grains) only gets 1,261 fps from that same setup, and an extreme spread of 37 fps.
I matched Longshot with Power Pistol, in both the 6" and 7" barrels...charge weights within a couple of tenths of each other, I'm pretty well convinced Longshot and Power Pistol are almost interchangeable, at least in the 10mm with 200 grain bullets.