I've got the 26.75" and would advise you to get it. I also have several 22.5 and use those too, but I can spatchcock a 20lb turkey and cook it indirect hot and fast on the 26.75 or cook a whole prime rib on there. Something you're not likely to do on a 22.5.
Team: Smitty's Real Pit BBQ
Superior SS-3 - Courtesy of Gainesville Jaycees and Superior Smokers
2 Custom Built Reverse Flow Stickburners
Weber 22.5" WSM
Weber 26.75" OTG
Weber Blue 2000 Stainless Performer