Wow, that is so good that it hurts to see. I have some vague awareness that the USP9 has a lightened slide as compared to the 40 and 45 variants that complicates optics mounting, but I didn't see anything at the link that was caliber-specific.
My new (to me) full rail Springfield is my current obsession, and I hope to fix it up into a 45 Super and perhaps eventually 460 Rowland field pistol. I reeallly want to see about a "big 9", and I've been casting about for the right platform, and this might be pushing me over the edge back into the USP.
I never should have let that first USP9 go.