Yes you can. That's how the 6.5x284 was developed. As any time you neck down from a larger caliber, watch your case neck wall thickness. If it ends up too thick you may have to trim the neck wall thinkness.
The 284 Win brass may be as hard to find as the 6.5x284 is right now.
IF YOU'RE SHOOTING DEER OR ELK AT 1000 YARDS, YOU'RE NOT HUNTING, YOU'RE SHOOTING.
THE SHOT IS THE TROPHY.