What is the purpose of this gun/round combo? From the looks of it, it suggest this is a paper puncher/target combo? I guess if you're going to punch paper inside 300yds, your velocity, or SD's wont make that much difference. Accuracy will rule. Im not a BR shooter, but understand they don't really care about SD as long as the accuracy is there. SD will become important at longer ranges though, but we're talking long range, and how precise do you want to be at those ranges. If you're SDs are in the 20fps range, unless you're trying to create one hole at 1000yds, I doubt it will make much difference. Probably none at all on plates out to 600yds. Others may have different ideas.
Bottom line is I'm not sure what you really want interpreted?
I do have one question from looking at a couple of the 5 shot strings...are you letting your bbl cool down sufficiently?
Do you weight each charge individually?
And, though I'm not a .308 loader, this "rule" holds true mostly across the board, or at least is my rule of thumb...use a powder that is fast burning enough to generate max velocity, but slow enough that the max velocity is attained at 90% or greater case fill. I think with the loads you listed, you're right at that with Varget. R-15 might be another choice. IMR 4064, BL-C(2) Also.