Good question. With my 28mm Spec. Armadillos the 28/35 (or 32 I forget) fit better than I remember the up to 28s working for 28mm Avocets years ago on another bike. Both worked in each case. I do remember not being quite as sure with the earlier tires with the respective tubes. Anyway 28s seem more like "true" 28s now-a-days, I'd say the bigger MAY have the slight advantage, just my impression, it may not matter much really.