you may be right in terms of smoothness, shcwalbe make big apples in 349 i believe, ive been on something called a raleigh RSW belonging to a friend - being big apples it also felt freerolling - up to about 12 to 15 mph - after that - regardless of what AtoB or anyone says, rolling resistance becomes an issue, for whatever reason, which is unfortunateI just got back from riding 16 km on a 12" wheeled folder (fat tyres) and it has a smoother ride on normal roads than a road bike with 27" wheels, on the proviso you don't drop the entire 12" wheel in a pot hole
There is one drawback to smaller tires they wearout faster.