I have a MK12 Mod 0 upper I built last year. It is very stable and with the Douglas (1:7) barrel fairly accurate...if I do my job it will shoot .5" groups. On the down side it is heavy...I do not have a scale or I would have gotten the weight of it for you. On the plus side it looks cool
I have the YHM Phantom flash hider on mine since I didn't care for the PRI model and it is equiped with a Nightforce 2.5-10x24 NXS on a Larue mount.
I have read posts in the past of folks that had this exact model from PRI and have been happy with it as always YMMV
Also; last I checked I believe Adco builds this style upper as well as a couple others.