PH, I suspect in terms of the ride feel it would drop somewhere between the Nomad and Mercury, probably bit closer to the Mercury, but I have never ridden either of them so don't know for sure.
The later mk5 club tour gets quite similar scores in the Thorn bike comparison chart to both the Mercury and the Nomad AB special, using the same 853 forks and wheel sizes. I think picking the right tire size, type and inflation level would probably make more difference to the ride quality than the tube types used to make up the frame.
From an esthetic point of view though, I do think the Mercury looks the nicest, much more photogenic, no dangly bits to spoil the lines!
I just get that nagging feeling, that once the shiny new bike phase passed, and the bike has collected the usual muck, minor scuffs and marks from daily use, there may not be enough of a difference in the way the bike looks and rides to warrant spending the extra money that a new Mercury frame and matching fork would cost.