I have always liked a five round group to show the true consistent potential of a load/gun combo... can't tell you how many times I cursed that fifth round!
Gun Tech - nice classy looking rig... I know with a dedicated bench gun weight is not of concern... but I can't help but think what a dandy Varminter that rig would make... a change-up in optics might be in order for that purpose... do you know what it weighed in at without the scope?
The two 8 twist loads that have worked well for me are;
Hornady 68 BTHP, 25.8/CFE-223, Win/CCI-SR, 2.350"
Hornady 68 BTHP, 26.0/H4895, Win/CCI-SR, 2.350"
Note those are single feed loads, you would likely have to mess with the OAL to magazine feed them.