I all reality the 6.5, 28, and 30's don't really do any thing the .270 can't do just as good. Not saying there bad because they are all very good calibers and cartridges. The .270 does not get the credit it deserves, it shoots a lot farther and flatter than what most think. If you really want to change barrels I'd go with a .270 with faster twist to get all you can out of the higher BC bullets. I have not did much studding on the Sherman cartridges but if you want some thing new but not a lot of work to make the brass the 270 Sherman looks like it would be fun. If you want a new caliber and want it for hunting and long range with easy to get components I'd go with the 30-06, but the .270 Win. will still do that too. But me being a gun guy I'd leave my first rifle a lone and buy another rifle, that way you would have two rifles to work with and enjoy and have fun with.