And if the OP chooses this I have some brand new cases for sale !7mm RM would fit the bill.
Personally, I think it depends on which type of copper bullet…. I would say a cutting edge/virtus/yewtree or any of the CNCd bullets have superior bc and virtus have different models so if you have either a lower velocity short range rifle (eg 300blk) or shooting out further choose one which expands easier (merlin). Id be very surprised if they didnt perform at those ranges but why not give them a message. I can tell you without hesitation all of the research you are doing has been done already by multiple factors. Virtus
I find my 308 very versatile. You cant go wrong with 308. Exceptional accuracy with above copper, and I use them when specifically required by landowner.
I wouldnt give upnon 6.5 yet-there are plenty of options.