PlayerScore 4.3.x will introduce the PVP Tab. Now you can view player vs. player information for all the players you run into in game.
The tab will display their current progress in rated battlegrounds, as well as th current season's Arena Team information. In addition, a break down of their performance in battle grounds and arenas in a whole will be displayed. The % values are color coded from red (terrible) to green (awesome).

Use this information at your own peril of course. Just because someone has 99% victory rate in WSG doesn't mean they are good in pvp. (Although it's an impressive value none-the-less). And somebody who has had terrible luck in battlegrounds may be an amazing pvp player. So be careful who you judge.

You can try out the newest features in the 4.3.01 Beta available here: http://forums.tentonhammer.com/showthread.php?t=56846