Esher Shore, there’s a recent post on Jan Heine’s blog where he questions all that and argues for fine herringbone treads. tbh as much as I respect the work they’ve done on some areas of bike performance I think it’s all getting a bit princess and the pea when you get into the tiny details of tread, going past scientifics and into simple feedback and confidence cycles, but he makes his points well as ever.
I’m not convinced either way, I’ll use the ‘too many variables’ get-out. Stability of a smooth rubber surface vs flex of any tread, vs the friction area of either, the variations in road/trail surface .. It’s all a bit complex and those debates are generally ‘won’ by those who make their points best – if there is a right in all that in the first place.
A vote for Marathon Mondials here, tough and a bit wooden but a really good all-roads tyre tread. Durable, smooth on road and suprisingly good off-road. Used the 47C version locally on all sorts of ground in winer or summer and they would be my choice for a big tour, no second thoughts.