Another option is to run OpenBSD current which at the time of this post has just been unfrozen and is very similar to the upcoming 5.3 release.
FreeBSD 9.1 uses xf86-video-radeon 6.14.3
and OpenBSD current has xf86-video-radeon 6.14.6
With current it is likely that your xorg will work out of the box
radeon(4)