@LightBulbFun I have a dump from a XServe with the XS31.0081.B09 firmware. As far as I can tell there is nothing exciting about it, it does not boot the X5620 that I put in to test, I didn't try other CPUs, but don't expect it would work with any others. I haven't had time to look into it further.
I had 5 with the B09 firmware, but got rid of the 4 working ones before I read your post and even realized there was a newer firmware. I notice all 5 of them had serial numbers starting with YM where all the other XServes I've seen start with H0. I believe this means they are from different factories. Also of note, the B09 XServes were made in March 2011 according to the serial number, where the latest B06 XServe I've seen was made in mid-2010.
I'm including the dump here since the XServe this came from is dead and will never be powered up (had to pull the ROM to dump it) I did test it by copying it to a different XServe, and it did boot up just fine. Curious if you or anyone can figure anything else out about this firmware.
Also my guess is the firmware isn't really 3 revisions newer than the XS31.0081.06B Apple publicly released, I think it's one version newer, the firmware version numbers were just mixed with the Mac Pro for some reason.
XS31.0081.B06
MP41.0081.B07
MP41.0081.B08
XS31.0081.B09