Rather than 243. AI, a friend went 6mm Rem.
That makes up into a very nice rifle.
If I were shooting any 6.5 I would set it up for 139-142 exclusively. I don't think the 123 will hang with it. Kind of like my fast twist 90 gr .223. The charts and software say it should shoot with a 175 .308 but it won't in live fire at long range. It is a hammer at mid range, though, the reason I don't see a place for 6mm in my rack.