Touring Tyres / Touring Tyre Size

I was fine riding with 20kg of equipment on a 25mm front and 28mm rear conti gatorskins doing John O'Groats to Lands End. To guys with us were running 25mm on the rear as well with no problems.

+1 to maxxis refuse (25mm) as well, the guy using them (Stallion) was the only person not to get a puncture for the enitre 1100 miles

That's fine but if you were getting a bike built like the op would you have it built to only take 25 mm tyres? You can still run 25 mm tyres but if you give yourself room for 32 mm tyres you have some flexibility built in.