Thank you sirs. I believe I was looking at those exact two scopes earlier today. It's good to know that I was on the right track. I will get to that mount shortly.
Others will reply with more specifics, but there is little difference in accuracy or velocity between a 16" and 20" barrel out to 500 yards. There is a thread somewhere on the forum with that specific information.
It is dependent on having the proper length receiver extension with the proper length buffer. As @jtallen83 said, a RE that is too long with a standard spring will still be too long with a Tubbs.
Parts list:
Faxon 18" match series barrel
Faxon BCG
Faxon stripped upper
Aero lower
Larue MBT
Odin Works Zulu 2.0 stock kit
Tubbs flat wire spring
H3 buffer (on order)
All other blue accents are from Strike Industries
STNGR 13.5" rail
Magpul bipod
VG6 muzzle brake and CAGE (on order)
I still need mags and ammo and to decide on optics.