Once I get as far East as the A6, there isn't any more flat. My 56 yo knees complain a bit on the 'up's, but my boyish bravado enjoys the 'down's. There are 2 really long descents on that route, and on relatively empty roads speed is easily built up and maintained. However the second one has one major issue, two thirds of the way down there is a crossroads, and as you are on the minor road, you need to remember to brake !!!
There is a set ride up here called the Bowland Badass, I've ridden about 80% of the route, ( accumulated over several rides I have to admit ), the only bits I've not done are the 2 biggest climbs, but hopefully I'll get them done soon. ( There's no way I'd try it all in one go ).