I have just rad this thread from the start and I haven't seen 6.5 x57 mauser .This is a Mauser proprietary cartridge which has been pretty much forgotten. The other hot shot 6.5s have overtaken it but a worthy cartridge.
I also have an 8 x60s
sold the 7x57 brno 600 but I'm still searching for a 275 Rigby and a 300 super
I dont own a 30-06 or a 308
I do have a 318 WR