I think the 6.5-284 shot better in the review, based on a statistically insignificant sample of one.

Article:
http://www.longrangehunting.com/articles/e.r.shaw-mk-vii-6.5-284-review-1.php

In the article John Barsness mentions:

"The 6.5/284 turned out to be more consistently accurate than my 6.5-06. The best loads from the two rifles shot about the same, with five shots in 1/2" or so at 100 yards, but the 6.5/284 shot very well with bullets weighing from 95 to 140 grains, while the 6.5-06 shot noticeably better as bullets got heavier. Why this should be so I don�t know, since both barrels have the same contour and the same rifling twist. (Maybe there is some magic in the shorter powder column of the .284 case.)"