Just because you can doesn't mean you have to. You can do 25-30 and put in 40W + whatever gravitational energy you need to gain (which will slow you down a lot

Just because you can doesn't mean you have to. You can do 25-30 and put in 40W + whatever gravitational energy you need to gain (which will slow you down a lot on the hills). But really, anything as efficient as an upright or more is fine.