OP, the 6920 is not an HBAR, it’s a 16" gov’t (m4) profile.
if the 6920 is all factory, that’s a great price
Many years ago my last range session with my M16 A1 it was 8 degrees with sleet and freezing rain ,everything was covered in ice, all weapons functioned. Can’t see the 6920 being an issue in cold weather.
Buy the 6920. Swap for the A1 since it is about the same length as the carbine in the 2nd position IIRC, maybe a bit longer. Sell the retractable stock assembly if you cannot use it and cannot see yourself moving to a locale where you can. With all that you saved over the other two put that towards ammo, some good hunting/defense stuff and some for practice. Put a VCAS or VTAC sling on it and maybe a light. Learn to shoot it and manipulate it.
The 6920 would be a good choice if you want a carbine gas system.I’d go with a new BCM 16" middy.
i’ve beeen wondering what you did about this. sure hope you had enough smarts to get a clean, low mileage 6920 for $850. that was a no-brainer to most of us here. let us know what you bought.
Yeah there’s a way, move down here to Virginia 
We have instant background checks… well almost instant; I had to wait 3 hours for the last rifle I bought, an LMT M4.
Here’s your direction sign: http://www.bravocompanyusa.com/Default.asp?Redirected=Y
Alternative route:
https://danieldefense.com/
A good Colt is excellent, but with the options offered by the two above makers, you can get exactly what you want from the start.
If you really want to buy a complete rifle local, get the Colt 6920 for $850 and don’t look back.
I ended up getting a Colt 6601c for 900$.
It works great and has had no issues after a few hundred rounds. I am glad that i bought a full lenght 20 inch heavy barrel for my first AR.
Whoever owned it before me has probably never shot more than 100 rounds out of it.
I couldn’t be happier.