Sounds like our OP is shooting from a bench rest, and in my own mind, if that is the custom purpose, I would select a 24 or 26 bull barrel. It would not be much good for a tote around hunting rifle, too heavy, but there is a lot to be said for a .264" bullet for deer sized game.
But if our OP is serious about long range Wimbleton long range type shooting at 1000 yards, best select a bigger caliber. With a .284 (7mm) bullet in a 160 grain boat tail bullet as an absolute minimum, or any wind will play havocWind deflection with group sizes. Wind deflection is directly proportional to a lack of a ballistic co-efficient.
I'm going for versatility more than anything. My current benchrest rig has a 22" Krieger barrel. Had it cut down from 24". I cant see me ever really owning a rifle with more than a 20" barrel as of now. I enjoy shooting long range but a true honest to God benchrest rifle is just too unwieldy to me. Not my cup of tea.
So I'm going for something that blends excellent long range performance with light weight, ease of handling, long barrel life and low recoil.
I cant argue the big bores are just wicked at long range. 338L and up really get it done. They also cost a damn fortune to shoot. 7MM Mag's are punishing in a light weight package. PUNISHING. My buddy used to have a very nice 300 Win Mag for his deer rifle. Note I say "used to". He just didnt like the recoil. Now he uses a .243.
So that pretty much leaves me in the 264 crowd. I dont want the recoil of the Mags, I dont want the weight of a dedicated benchrest gun and I dont want the lack of accuracy you see in a plinker.
Going with a 18-10" barrel in a lightweight package using a 6.5 bullet just makes good sense. The 6.5x55mm is used for moose hunting in Europe. The 6.5x284 is about the top performing long range round unless you go big bore. The 260 is a great light recoiling hunting rifle.
Regardless of the flavor, the 6.5mm round is just an excellent, versatile round. It does everything well and nothing poorly.
So my goal is a 6.5Grendel for my AR15 and a AR10 chambered in 260 and if I ever come across stupid amounts of money a Windrunner in 260 for shits'n grins.
ETA:
Corrected my number. I typed 264 above as 284. Dur.