If I were you, I'd just do a straight 6BR. Tune the mags, time your cocking piece, wear in your TL3 and it will be a slick feeding, smooth, pleasure to shoot. Predictability and consistency of load over 2000rds is not easily quantified by most shooters but in my mind it counts for a lot.
As far as speed goes it sounds like you have an arbitrary number you want to get to. If you try to run a BR at 2900 plus out of a PRS length barrel you're going to turn it into your 6 Creedmoor more. Run a 105 at mid 2850's in a 26" barrel. For anything under 1000 the speed difference only shows on paper. It will not handicap you over your marksmanship, mental game, or wind calling.
You could pick a Dasher, BRA, GT, XC, whatever and they would all serve you fine. But if you try to run them at an arbitrary speed YOU are going to induce problems that aren't the cartridges fault. Run a 6Creed at 3000 flat with a DTAC with a mild load of 4831SC, RL23, RL26, or H1000 and it will get you a solid 1800+. Run it at 3150 with 4350 and now you're looking at that short barrel life it's famous for.
As far as fireforming goes, hmmmm....let me remember....it's been so long ago that I formed my Dasher brass...was it a pain in the ass? I've had it for 4 barrels. I seem to remember fireforming at practices or a club match. Was it difficult...?... Don't really remember