One former Pacer turn which could be fun was the FGW 143 on the 09.33 Exeter St Davids to Cardiff Central and 1300 return: 2 hours 45 minutes each way with extended periods of maximum speed running on top quality mainline track. While Pacers are undoubtedly cheap and nasty I've always found them to be perfectly tolerable on welded rail away from pointwork provided the suspension is in good order with unworn wheel profiles. Thrashing up to Whiteball summit flat out in bright sunshine with a HST in your imagination chasing hard on your heels made for a pleasant interlude during an ALR! These days the outward morning service starts back from Penzance so I would expect that anything other than a 158 is a rarity.
As for the Cumbrian Coast I know that at one point Northern's diagrammers created the turn to assist in local traincrew maintaining their traction knowledge. As they get withdrawn from service in the coming years it'll be interesting to see how their "empire" is scaled back over time.