I have had many 1-14 .22-250's. I started when it was still a wildcat. I have used bullets as light as 36 gr. and heavy as 70 gr. Speer. I had one 1-8 twist. It didn't really shoot anything well. When I am hunting I don't have time to range, twist knobs, and get on target. I like the speed of 50=55 gr. bullets and they do all I need for hunting. I suppose it I wanted to shoot steel at long range there would be a benefit. I don't. So the fast twist is like the 6.5 Creedmore. A great gimmick for selling stuff.
I don't think that the 6.5 CM is a "gimmick", as it does what it is advertised to do and does it quite well with factory ammo.
Being a 260 REM guy, I believe that the original 1-9" ROT 260 will kill things as well as the 6.5 CM out to a range where shooting a longer VLD style bullet is necessary. A 260 REM with a 1-9" ROT barrel will shoot 130 grain ABs just as well as a 6.5 CM with a 1-8" ROT barrel will. The 6.5 CM win the race because there have always been better factory loads available for the great majority of hunters who don't reload and don't have sufficient shooting skills to reliably take game at ranges that are often far less than a 1/4 of a mile.
