I can only speculate on why triumph changed the cams on the 865 motors, but I would suspect that emissions were part of it. On the 865 cams the lift is substantualy less and there is no overlap.
While the 790 cams are superior to the 865s, The t-bike cams are not the same as 790s. somewhere, I think on the ratnet the 790 cam spec are posted. I measured up my t-bike cams before installing them and they are not the same as the 790.
that covers half your question (sort of)
