Thanks for the input Chaps.
All things considered I'll run TKC80s with Michelin 4mm heavy duty tubes filled with Ultraseal (or similar). Should be pretty resilient agains pinch punctures when riding soft with low pressures, but capable of 80 mph on tarmac when inflated normally. May get a bit of wobble and weave, but I'll have to learn to live with that. Also taking a couple of puncture repair foam/slime canisters, a spare tube and a spare rear tyre.
Hoping for about 6000 miles from front and 3000 from rear.
Thanks