Higby broadcasted last night in-game to change render distance in your Useroptions.ini file to temp fix FPS issues until they can patch. He also said they think the issues are related to tanks specifically and asked that players limit the use of tanks to help everyone's FPS.
EDIT: Just found this stickied beta forum thread too:
FPS Performance Issues 09.21.2012 Patch
Lot of posts in there but I did see one post by Hackney about this being a bug and they are looking into it. Not to mention Smed all over Twitter saying they are working on it and it is a bug from latest patch.