I have extensively tested the 7mm GPC (nearly identical to SAC's 7mm Creedmoor) with barrels from 23" to 28" I have personally found H4350 to be the best performer overall with heavier bullets. Superformance and RE17 will give a significant edge in the velocity arena while Varget and 8208 give great accuracy but build too much pressure before reaching maximum velocity potential. If you want the best combination of accuracy, consistency, and velocity H4350 is the way to go. We have built a few 23" lighter weight hunting rifles, they have Krieger #5.5 contour barrels. The 4 groovers make about 2750FPS avg with 44.9 grns of H4350 and 168 vld's while the 5 groovers are a touch slower. This is using hornady 30TC brass necked down to 7mm and F210M primers with an OAL of 2.810+/- I have also done alot of load development with Lapua 308 Palma brass neck downed, resized, and fire-formed which i prefer but it is a lot more work. The load is compressed but with the proper neck tension very accurate.