Audax rides

for the 300k I'm thinking of doing A Rough Diamond, look fun, any other suggestion?

This is a very fast route, ideally suited to those that want a good all-day ride, or those attempting their first 300.

Only three controls, but lots of places to stop if needed. Easy to navigate route with stunning views and scenery. Good quality controls all with hot/cold food & drink available.
that does sound very enjoyable!