I usually catch the 09:15 PLY ex 07:10 ex PNZ, it's usually running late after SER and tends to lose more as it comes up through Cornwall, sometimes with some smart work at Plymouth we get an on time departure, but not always and rarely make up time, especially if there are any TSRs en route.
The last time I caught it our train was 10 cars sitting in platform 5 and the 5 car PNZ portion came in on ^ and they had to de-train and cross the platform, with all their kit, utter chaos, 29 minutes late at RDG, my destination.
As Gwiwer, above says, down trains rarely leave PAD on time and continue to lose more, even on the juice! By the time they get to RDG.