I show the tougher, western side of the Marie-Blanque to be about 43km. The easier, eastern side is only about 30km. The 7.5% average of the western side doesn't sound bad but the first 4km are rather easy. The last part is tough.
From the north, the Soulor starts about 29km from Pau but it is very easy for 10km. The actual climbing starts at about 39km. That is also, roughly, where the Col de Spandelles starts.
Like Big Ring mentioned, a Spandelles/Soulor loop would be good. You could also ride the Spandelles into Argeles-Gazost, the climb the Col de Borderes. The Borderes sort of parallels the first of the Soulor but the profile looks a little tougher. Then, the Borderes rejoins the Soulor when it starts to get steeper in Arrens.
There is also the Col de Castet. Starting in Louvie-Juzon, it is only about 26km from Pau. It is not a particularly big climb and does not go anywhere so it is just and up-and-down climb. It goes up 452m in 7.7km but the first 3km are very easy. The last 3.5km though are 9.3%, 10.5%, 12% before easing off to 5% for the final half km.