SUW is 265 miles…theres a guide book with enclosed sections of landrangers covering the route,it includes local history and info on views etc..i rode it in i think 1992,got the train from dunbar near its finnish down to stranraer via glasgow then 6 miles to portpatrick on road,took 5 days including the train journey down,from its end.
i remmember some of it was a bit grim going but i loved the isolation, i hardly passed any walkers till moffot onwards,where it also got better under foot/wheel, i only had a 4 mile ride home to dunbar from its end at cockburnspath where trains stop for edinburgh west or south to newcastle…i imagine its all mostly regraded and pathed now,it is all ridable from st marys loch to the coast anyway,
if you can find trailbike magazine (tbm)issue 85 sept,2002 from there back issues theres an article on someone i know who did the whole SUW in a single day on a motorcycle with a few diversions on other trails where nessecery (boggy sections etc..) to raise money for cancer (maggies centre edinburgh),took 14 hours (including a 255km road ride from the lothians)