There was a whole range of eXp's. It started with derailleur-geared eXp, and ultimately they offered three Rolloff versions if I remember correctly. There was the regular eXp, the eXpr (narrower clearances for skinnier tyres and fast touring), and the eXXp (with the option of suspension fork). If you search the forum, you should find Dan's post with archive brochures for all these models.
Even when they did offer custom builds, Thorn philosophy was that their off the peg frames are fine for the majority if not all cyclists. I seem to remember a brochure advising to always upgrade the spec, rather than splash out on custom build. Kevin's frames were super-nice (I got one!) but whether worth a grand extra... Probably not for the majority of Thorn's clients.