Continental do the Grand Prix in a 406x28:
Conti Grand PrixBut I haven't tried them.
I've had Stelvios and Marathons on my Moulton. I can't really tell the difference, in terms of rolling resistance, between them. The Marathons are 40mm, IIRC and 100 PSI.
I also have Conti Top Touring in 406x37mm, but these aren't made anymore, and their replacement (Top Contact) are not available in that size. Edit: Contact are available in this size but the rec PSI is somewhat low:
Conti ContactEdit 2: Conti seem to do loads of tyres in this size. Here's another:
Sport Contact