Hi Phil, I've never tried more than six slabs on mine (rolled 3 on each level). The rack I have only holds 3 also (6 halfs), but you may be able to rack 3 and roll one or two on same grate. Only way to find out is try 'em on for size!
Between the rib rack and rolling/coiling the rest you should be able to fit them all on there for the first 3 hours at least. You might want to fire up the performer though for the 2 and the 1 though. Make sure you have enough fuel thats a lot of meat. I have done eight racks before all rolled/coiled 4 on each grate.
I did 7 a few weeks ago and I think if I had been creative I could have done 9. I did the 3-2-1 however I did use my gasser to finish them up. Here are a few pic's. Vince