To be honest anything silent gives you an edge over other players, you don't aggro the zombies when shooting so there isn't any tell tale signs of player activity. Once you've spotted a enemy player you can shoot at them without giving away your position (no muzzle flash, virtually no noise etc..) and generally get the kill before them knowing you're there.
I'm saving the MP5A5 SD for a clan mate, I'd prefer a DMR as the M4's companion, though I'd not pass up on a M107 
The thing is though, MP5 has low range and isn't very deadly, which doesn't make it ideal for PvP. Any assault rifle will kill from further away and also quicker. If you can sneak up on someone, you should ALWAYS get the kill before they know where you are. Silenced M4 is a sweet compromise, though. Good range, lethal enough, silenced. But I still love my completely plain M16!
M107 makes fuckloads of noise and can't be used with NVGs, it's alright otherwise. The new M107's that spawn can also be used with backpacks, the ones before couldn't.
Still, assault rifle gameplay >>>>>> sniper gameplay. The firefights are a lot more fun and doesn't matter if an enemy pops up from a bush next to you. You'll also be moving in and doing stuff instead of sitting in a bush with your sniper rifle, shooting at people who don't even know you're there.
