Thanks for all your suggestions. Shortlist came down to Nobby Nics and Panaracer Fire. I've taken the risk on clearance and gone for Nobby Nics because they have had more iterative innovations giving me the feeling that they might have the upper hand in performance, technology, and execution. If I struggle on clearance, I'll fall back to the Panaracer Fires.
I couldn't quite get my head around billy bonkers' little teeth and how they wouldn't just turn into slicks in mud.
Panaracer Smoke/Dart are widely liked off road (again from mid 2000's comments IIRC), but some suggesting they were draggy on tarmac.
IRC Mythos - I didn't do enough info research to get insprired (e.g. don't know about compound performance, or how widely well recieved they are)
Marathons, Land cruisers etc - While a knobbly tyre can be a drag on tarmac/dry trail, you can keep going. However, wheels spinning or slipping in mud can bring everything to a halt or make things sketchy. For me, sub-optimal performance on long distances of hard surface doesn't drag me down, but getting stuck or falling in the mud can make me a bit miserable within an instant. So I've realised I've got a bias (rigthly or wrongly) to veer towards the knobbly end of the spectrum.
Magic Mary - I got the impression that this might be overkill or not targetted at my riding. Perhaps intended for a more aggressive, specific type of riding (gravity).
