I tried out an SMG with silencer and semi-auto mods, and I'm quite happy with the results. The biggest advantage is fire rate. When I was sneaking around with a compound crossbow, it didn't really even register how much time I was spending waiting for it to reload. Now I can pop 40+ zombie heads without having to reload, and cumulatively I think it shaves several hours off my time to clear a Tier V POI. Because I'm going all stealth and it's so quiet, it's not a big deal to 'double tap' soldier zombies or other, stronger enemies as needed. I can also switch to a knife or other weapon when I know 1 SMG bullet won't do it. But that's the exception - most zombies are dead with the first shot. As far as I'm concerned, we have a winner!