I was going to say got to
http://www.international-benchrest.com/
click on the MATCH REPORTS, then LONG RANGE, & look at equipment lists, which include bullets used. But a lot of the reports don't seem to have equipment lists.
I took a look at a few anyway, and the little that I saw for 6.5 used the Sierra's & Berger's that you find at 1,000 yard matches. Also used at 1,000 yards are Clinch River, but they are less common -- Greg is a small manufacturer, and the bullets can be a bit harder to get.
The A-maxs have had a history of being , well, inconsistent. Hornady claims to have been working on that, but long-range brenchrest shooters are apt to stick with what has worked in the past, so any return to test the A-max's will probably be a slow one.
You might take a look at the NBRSA 600 yard match results. I believe some NBRSA shooters on the west coast are using the smaller 6.5s with good results; maybe they have match listings showing A-max performance.
FWIW