I think the Panaracers are quite slimline for a 25c tyre - I like a racey feel though so they suit me. Have you tried mudguards as flush to the frame as possible? I seem to remember having to play about a bit to get them to work but there's plenty of clearance now. Well, i don't suffer from annoying rubbing sounds anyway (from the mudgurads or anywhere else!)
John - I'm not sure many bikes would shimmy at 35mph - this was probaly more like 50. I don't necessarily blame the frame; shimmy seems to be a fairly random occurrance and dependent on rider weight, position, front/rear weight bias, tyre type and pressure and so on and so on. When the system starts to resonate it's difficult to stop it. You do lose your confidence in a frame when it happens, however illogical that may be. (Load was a small firmly fixed under-saddle pouch and large rear jersey pockets btw - I'm not quite as minimalist on 600s these days but I believe in carrying the minimum necessary on audax rides!)