Is there some setting I have overlooked??
Well, you are using the wrong program? Forgive the sarcasm, but despite all that stuff PS simply is not a video editing app and all these features have to work within the normal limitations of the main program, meaning it is chewing through the frames as if they were still images plus there is a definitive bottleneck decoding footage in the first place, expanding and flattening the buffers and then re-encode it back to a video format. Most of that happens in a single thread to provide temporal consistency, so there you have it why your (theoretically) powerful CPU is sitting on its own hands with nothing to do for the other cores. Come to think of it, if you recorded at 120 FPS your 68 minutes could equal almost half a million HD frames and batch processing an equal amount of images would take just as long. And there is tons of extra overhead with PS creating lots of temp files eating up your transfer bandwidth, possibly color management stuff requiring extra processing and what have you. So more or less, I suppose you will have to live with it or consider using other "proper" video programs like Premiere Pro.
Okay, I realize PS is not optimized for video, but I did not expect it to be glacially slow! Sure, Premiere would be a better choice, but I seldom edit video and it would be big time overkill. Since I have PS, just thought I would give it a try. Thanks.