I am inclined to believe it would go up rather than down.

I am basing this on the following post. Scroll down for Blue Post.

http://forums.worldofwarcraft.com/th...sid=1&pageNo=1

I hope I am not just being overly optimistic.
that post was in response to AV in the 51-60 bracket, where XP does suck ... the 71-80 bracket grants significantly more XP.

Blue post here talks about XP changes in AV (see player vs player heading) : http://www.mmo-champion.com/index.php?%3Btpstart=10