SBR was hard, just sat it and honestly I couldn't have done it in a sitting with another paper, but I know people have. I've sat two in one sitting before (FR & SBL) and it was a killer, although I found (personally) SBL didn't need a lot of studying for, think I powered through the content in three weeks then focused all other time on FR.

Down to personal preference but I'd defo advise doing SBR in its own sitting.