Thanks for the plug, but only the most stable/regular NMT pathsOther than that, I would suggest signing up to or buying a copy of Freightmaster which provides details of the NMTs' times.
As far as the East Coast main line run is concerned, the NMT has a regular fixed path on a weekly basis that is well known to many enthusiasts along the route. I believe that this is similar for the other routes that the NMT operates; it has a fixed rotation schedule although not all routes are covered on a weekly basis. For this reason the NMT is usually a lot easier to predict than other test runs which appear to run on a more ad-hoc basis and cover lines more intermittently.
Other than that, I would suggest signing up to or buying a copy of Freightmaster which provides details of the NMTs' times.
TIC, MENTOR and TRC can all do 100mph when transit or testinG, formation depending, normally 90 due to running with 90mph locos. All can run as Class 1. The NMT runs in the WTT because it does predictable, regular and dull mainline routes. The rest do not, and are STP trains - hence unpredictability.
UTU are indeed very slow, due to the 30mph restriction when testing because of the RSU equipment in contact with the railhead. They normally run at night because of this. SGT is also limited when testing, to 50mph.