Dan, that's a tremendous amount of knowledge and information on file; as always you've overfilled your quota. But I don't need new mudguards yet, just to heed the warning to look after my P65s because they may not be available in future. (Blue smoke break while I stick pins in a wax model of the SKS marketing director.) You can forget those beautiful Honjos for me; I speak confidently of engineering from years of ad hoc industrial design, but I'm an artist, not a craftsman; I'll never get them on straight, and the guy at the only LBS is a blacksmith, not a fitter, and anyway he's 83.
I think, anyway, that when the P65s go, I might try the Planet Bike Concordia 29er mudguards well before I go to metal mudguards. My bike is not cosseted. I don't think, as some have said, "That's a bike for BMW money — you can't ride it into the rough!" My way of thinking is, "I buy the best, and I expect it to survive my kind of service, whatever I want to do, wherever I want to go." It's one of the wonders of our age that pretty limp plastics are more durable than hefty metal. To make my P65 last longer, I've decided not to mess with them, not to fit longer/heavier/stiffer/dicier mud flaps, but to make the short mudflaps I have now do. Today I deliberately rode through some standing water at speed, and from the water on top of my shoes, I reckon I need only one inch extra on the mud flaps; maddening, but my decision is made. (Pass up more pins, and maybe we should have wax dolls of the entire board of directors of SKS.)
Pity about the Berthoud's being too narrow -- that thread you referred me to is about 26in wheels, and it isn't quite clear that the guy who says they will fit has any experience and isn't just reading off the sales table referenced in the first post of this thread. I've long experience of buying components that Peter White stocks, if not necessarily from him, and have always found him to offer spot-on info, so I think it much more likely that your first assessment was right, that the Berthouds will take only what today we'd consider medium touring tyres, around the 37 to 42mm range. I like the idea of stainless mudguards but I don't have time to fiddle with projects, I want stuff that fits right in at most an hour of work by the ten-thumbed (my 8FUN electric transformation from the eponymous firm in Britain is a brilliant example of a properly developed kit of parts, see
http://coolmainpress.com/BICYCLING.html ).
Andre Jute