Well, as far as range, 9x19mm is good to around 100 yards without *much* holdover, and this is similar velocity (your subsonic load) - just a heavier bullet with a better BC. So your PBR will be that or a bit more (maybe 110-120 yards PBR for a man-sized kill zone would be my guess; possibly a little less; 80 yards easily though, for a 6" [+/- 3"] kill zone).
If you know your holdovers, then it could be quite effective out to 400 yards or more pretty easily, albeit with a lot of drop. But it will retain the majority of its (small) initial energy with the very high BC and heavy bullet, for a looooong ways. Just have to know your drop & drift, like anything.
Accuracy, of course, is a function of barrel quality, chamber specs, crown, ammo quality, etc.
FWIW, I'm very interested, and have as one of my next 4-5 guns to acquire (very high on my "list"), a .338 spectre - but mine is going to be a turnbolt SBR with about a 10" bbl & can, probably on a Savage action, with a 1 in 6.5 bbl, to stabilize 300s+. I can't see needing or wanting more than one immediate shot from such a rifle (I'm not an 'operator'), and it will be quieter and possibly more accurate as a turnbolt than a semi. Not to mention a lot cheaper to build, and easier to retain your brass. Mine will be strictly a range/fun gun.
http://www.teppojutsu.com/
This seems to be the better goldilocks choice than the .300 whisper/fireball or the .500 phantom, since the .500 phantom is just too danged expensive to shoot, whereas the .338 spectre will give you a pretty big boost in power & BC over the .300 whisper (comparing subsonic to subsonic), without much added expense. And a good 9mm pistol suppressor should be useable, at least with subsonic loads.