To me, cartridge efficiency is a pretty big deal. Some chamberings are just too overbore so while they can get impressive velocity, it takes a lot of powder to get there and similar chamberings with a bigger bore can get the similar velocity with a heavier bullet with the same amount of powder.
The picture in the last page saying that Constructor had stopped developing any 6.5mm wildcats larger than a 6.5 BRX for short barrel guns kind of displays that. He said bigger cases wouldn't increase velocity more than 50 fps in a short barrel.
I believe him because I have an 18" TAC6 barrel he made that shoots 105 grain bullets faster than a 22" 224 Valkyrie shoots 90 grain bullets. It's the same parent case and the BC of a 105 grain 6mm is almost equal to a 90 grain .224 so it's ballistically superior out until around 950 yards and then the Valkyrie has slightly longer legs for target shooting.
I think the ultimate balance happens when you shorten a barrel, increase the bore and go down in weight class for bullets (it will be higher in grains but a 90 grain .224 is about as heavy as it gets, a 115 grain 6mm would be its equivalent so a 105 grain is actually a good step lower in weight class).
You just need to juggle numbers to see what kind of energy you need down range and choose an efficient way to get there.
Since I like efficiency, I go for long barrels also but I went with 284 Winchester instead of 6.5x284 and I went with 338 RUM instead of 300 RUM or 300 PRC for my two latest builds and i think they will have the ballistics to shoot steel at 1 mile+.
I would never build a 16" 6.5 PRC and if I was dropping down to a smaller case, I would choose 6.5 Creedmoor instead of .260 mostly because of its popularity and ammo availability but I think 7mm08 or even 308 might be a lot more efficient in a 16" barrel.