There is definitely a correlation between velocity and neck tension..the more tension the more pressure I believe the guys at Barnes have played with this extensively
Next scope over here will be a ZCO without question the TT are also a superb scope and you really can't go wrong with Nightforce either ..at the price point you are talking about id buy the one that looked best to my eyes and dsicount what others have said ..i just wish there where more light...
We have built quite a few prcs if your going light id stick with the 6.5 its much more enjoyable to shoot in an 8lb and under configuration..the 6.5 pictured weighs 8 lbs for reference
Pretty big fan of a switch barrel set up for this application that way everything but the caliber is the same ...we built my 9 year old a .223-6.5 prc switch and it makes it really easy for him to get used to the scope, stock ergonomics, and trigger control while not being concerned with...