As it’s unlikely you’ll get many responses, I’ll try giving a guide- this isn’t 100% but hopefully it’ll give you a rough idea.
Traction: 37s, 57s, 66s, 68s (Possibly 88s as well)
Wembley - Crewe
Wembley - Dungeness/Sizewell/Winfrith
If you’re also considering GBRf at the same location, I believe they do the following:
Traction: 66s
Wembley - Crewe
Wembley - Felixstowe
Higher link adds Class 92 and Euston/Crewe-Preston for Sleeper work. Also, you may sign units for testing such as GBRf are currently testing the Class 800s and Class 755 Stadler units.