I can get 6 racks flat on my egg with the extra rack. If it were me I'd just try and fashion a 2nd level on the Primo, or build a UDS. If you're feeling lazy then buy a 22" WSM.
"I can get a good look at a T-bone by sticking my head up a bull's a$$, but I'd rather take a butcher's word for it". - Tommy Callahan III
XL Big Green Egg, 22.5 Weber OTS, WSJ Gold/Mini WSM, 18" & 22" WSM, UDS "No.8"
Flyers Orange Thermapen
Napkin Killers BBQ