High Damage, High fire rate guns like the TAR-21 and AK-47 are barely effected by stopping power, you probably won't realise you're not using it. Just don't silence them.
Also the UMP45 does not need Stopping Power ever.
I silenced my TAR-21 with SOH, CB and Ninja and I still barely notice.
I noticed this thread has too much UMP45 and Scar-h.
Vector is very viable without SP, as is the P90 and if you're good the Mini Uzi. I rarely use the UMP45 so I usually use Vector or Uzi and they're very good up close. Due to high rate of fire and low recoil they don't need SP, even with a silencer.
For secondary, SPAS-12 or handguns. If you're using deagles or usp.45 akimbo use steady aim.