After over 20 years of service in uncle sams lil social club I tend to look at things a lil bit differently than most of the younger generation and if you can't see the backside of 65 ain't much chance of me bein your son there pops

, unless momma got busy alot earlier than she told daddy

, (and she wants to talk to you about 18 years of back child support sport) but be that as it may.
Your choice of words might confuse the youngens, as I have said in the past anything that can put a golf ball size hole through a man is no toy I my book it is a lethal weapon and in this case a weapon of war (never did have to much time for toys, to busy on the triggger of a M-60 or M-2 I guess...mispent youth).
Anyways your choice of general varmit control for around the ol home stead is very nice, my current choice for a meet and greet in a hallway is the Saiga-12, now if your lookin for nuthin but pure high speed low drag FUN !!! (you gotta get one of these before the next imperial dynasty oops I mean election).
So to sum things up for me at least the 51 or any of the clones from 6" to 12" is a very effective argument ender in my opinion, in this cal. the selection of bbl length is more a matter of personal and or mission preferance.
The 7.62 NATO (or .308) WILL LOSE some velocity and energy the shorter the bbl but at CQC range out to maybe 100 to 200 meters it's really not going to make much of a differance to your bullet stop, as I said the standard SA 7.62 147gr FMJ cronos out at approx. 2,000 fps that translates into approx. 1,500 ft-lb of energy at the muzzle, just a tad shy of the 7.62 X 39 out of a 16" AKM at half the bbl length.
So say what ya want, shoot what you like and be happy, as for me if I gotta take only one rifle out into the vast wasteland we call civilization i'll take my V-51 everytime.