Hi Dave,
I used your technique:
Sync up 2 hour-long clips; lock the bottom clip.
Every 30 seconds split the top clip with the razor tool
Delete every other section of the top clip.
THEN
I copied and pasted the split, top clip over the top of my next video and whilst it was still selected pressed delete.
This made all the splits instantaneously!
THANKS FOR THE HELP
Rory