Seems to me the only way to answer this question is to chamber the same barrel for as many different cartridges as possible and see what happens, a few different times on a few different guns.
Also, the comment about benchrest shooters ending up shooting the same cartridge pretty much says it all. Cartridge does matter.
I had a 222 mag in a Sako Vixen rechambered to .221 Fireball and it shoots better as a Fireball for whatever reason. But maybe it's me, maybe it's the loads.
For my money, the benchresters prove that cartridge choice matters.
