Owning rifles in both cartridges I would opt for the 6.5x284.
It will kill everything the 264 Win can out to 1200 yds.
50.0 grains of RL17 will fetch you 3,000 mv with a 140 Berger VLD.
The 264's, and I love them, can be, in my experience and I've owned 3 of them,
a more finicky cartridge for accuracy. In contrast the 6.5-284 seems easy to get
there, with less recoil.
Unless you plan on killing out past 1200 yards I seen no reason for a
case that holds more than 70 grains of powder. In that case your recoil factor just went up.