I would like your comments of the differences and advantages of a standard 6920 and a Lewis Machine and Tool MRP set-up.  Both would have the 16" barrel but I would opt for the "enhanced" bolt carrier group.  My main concerns are reliability and accuracy.  The rifle would see triple-duty as a LE patrol rifle, hunting firearm and plinker.

Besides the full-length rail system, how would you rate each one in a comparison and for those who own MRP's how is repeatability when removing/replacing barrels.  

I've never pulled the barrel on my MRP, but MSTN and others have measured POI shift of about 1/2 MOA, IIRC. My MRP and my brothers 6520 (only Colt rifle in the families stable right now) are both very reliable, so long as the MRP barrel is properly installed. Be careful to torque it properly. The accuracy edge theoretically goes to the MRP, because its floated, but thats an easy fix for the Colt.

I have both the MRP 16” and a Colt 6920 16” and here is what I’ve noticed.  The MRP is heavier.  I have the rifle length upper, but even if you go with the carbine length, there is more rail and a heavier barrel contour.  But this isn’t necessarily a bad thing.  The MRP also has less felt recoil.  This could be due to the extra weight, but may also be in part to the midlength gas system.  Most will agree that just about any 16” barrel with a carbine length gas system kicks more and is harder on internal components.    

I personally haven’t tested the POI shift either.  But, any time you do major maintenance on your rifle you should check zero anyway.