The 26" doesn't sound that much larger, but it is. The extra real estate is great and it feels more heavily constructed than my 22". The lid also sits more vertical than on the Performers which is a complaint on the Performers a lot. I would alsways go bigger, if you aren't cooking much just start a small fire on one side and cook direct over it.
XL Big Green Egg, Weber Performer Platinum, WSM 22.5"