The cartridge that this argument applies better to is the SLR family. The 6.5mm slr takes a 260 shell, squares off the shoulders by pushing them back and you lose a grain or 2 of powder while getting a square shoulder and longer neck. It has often been said that the longer neck keeps heat off the throat...it makes sense but I haven't seen any real data showing it is more than a theory.
Being a fan of the 6mm SLR I've wondered about the 6.5mm version. I do like small to medium 6.5s and the SLR looks a very attractive option.
To me, common sense dictates that as you approach 50g of powder, fire cracking and leade growth will increase no matter what kind of whistles and bells you have on the case or Bones from a dead black cat you may have in your pocket. Perhaps cooler burning powders are your only salvation.
I burn more and more Viht N160 and N165 these days in my favourite cartridges. It's too early to know what it does for barrel life with my loads, but present indications look good. The biggest issue / problem with N165 in medium size cases is simply getting enough in! Just OK for 284 throated for bullets seated well out unless you want to hotrod the cartridge, but much too heavily compressed in 7mm-08 (long freebore) even in thin-walled / higher capacity Winchester brass.