Another question for John: What's the Mawddach Trail like for 25mm tyres? I notice you take us along there after Barmouth bridge.
I've happily ridden it on 25mm tyres with no problems. It's not tarmac'ed, but its a firm surface, not much loose gravel and pretty smooth so you can rattle along quite nicely. You're also likely to be there at a time of day after all the tourists have gone home so you can have it to yourself rather than dodging prams, dog walkers and newbie cyclists.
If the weathers good the views are superb, much better than the road which runs slightly inland and is surrounded by trees so you hardly see anything. The road has a couple of lumps in it as well, so overall I'd say there's not much difference time wise.
