I recommend 26" barrels as a minimum on all magnum cartridges and, in fact, I try to talk my customers into 28" barrels on custom barrels. Personally, I run 29" or 30" on my builds, but also have 28" and 32" to choose from.
I don't use brakes generally, have all of ONE so fitted rifle, but it needs it.
My 375 Weatherby could use one, just to tame muzzle jump, but I can live with that, and I don't feel ANY 264WM needs a brake, but that's a personal preference.
I will add, I built 2 rifles in 25WSM and one in 6.5WSM. They were plagued with pressure excursions, the 6.5 was a little less affected than the 25, but all 3 rifles were a nightmare to tune without known data out there. We had to extrapolate loads from the 257 Weatherby, and even then we had case dents, sooting and then locked bolts and blown primers. I realise this was when there was much less powder to choose from, RE25 was the slowest available and the only powder that actually didn't behave badly.
The 264WM is a known cartridge with plenty of data available. This is what I recommend.
Cheers.