This is one of those 6 one way half a dozen the other. They are near mirror images of each other ballistically, with on the average, a slight FPS advantage going to the 6.5-06. I think the 6.5-06 case only has something like 2 water grains more capacity than the 6.5-284 does which is almost a moot point, IMO.
Anything off the 06 case feeds like butter that's for sure but I've got a 6-284 and I've NEVER had a single feeding issue with it either.
IMO, the fact that they are so close to one another and you can get 6.5-284 Lapua brass ready to shoot right out of the box would push me slightly toward the 6.5-284 and 1 box of Lapua 6.5-284 brass would last you nearly, if not, the life of the barrel.
One thing is for certain, you can't go wrong with either!!!
The 6.5x284 with norma brass holds exactly the same h2o as winchester 30-06 brass or 1.1 grns more than winchester 25-06 brass, when necked up to 26 cal with the cases listed the 6.5x284 holds .5grns more powder than the 6.5-06. Plus the short fat rebated case of the 6.5x284 with its 35* shoulder is more efficient than the 06 case, the 6.5x284 wins velocity wise until you go to the 6.5-06AI then there is 3.5-5grns more capacity. Another thing is a loaded 6.5x284 round will be between 3.1 and 3.2" oal where the 6.5-06 will likely exceed 3.6" oal but neither is a problem in a LA remington. Anyway my vote goes to 6.5x284, its one of my favorites.
the 6.5/.284 is a great round for sure, but if you check the 1000 yard shoots the 6.5-06 is much more common. Why? I can't say, but it is. The 6.5/.284 is well known to be hard on barrels, and I doubt the 6.5-06 is easy as well. Still I think it will be easier on them. But in a hunting rifle, you'd never see the difference. The one thing that has always bothered me about the .284 case is availability. I've seen them dry up twice now, and there'll probably always be 30-06 cases laying around. The one serious advantage the .284 case shows is the length when used in a longer action. But on the otherhand it's neck is too short for the caliber. And I think a 6.5-06AI is probably a lot better round in the end. Still for a hunting rifle, I think it'd be hard to do anybetter than the 6.5x57AI. The others are faster, but each has a drawback. The 57mm case length allows big long bullets to fit nicely in a magazine, and cases are real easy to build (just neck up .257 Roberts cases and fire form). Of course you could solve all this quagmire by simply building a 6.5WSM