‘Back in the day’ when I used to do testing the P901/10 was the quick course on the south coast
IIRC it was 4miles ‘up’ over a flyover then 6 miles of gentle downhill
All on a dual carriageway getting a nice tow from everything. About 60s quicker than a normal course.
When I got my first pair of clip on’s ~ 1995 it improved my times by about 10s/mile
Sod doing it again now though :p