i find waist good for both Altura shorts in small. ok Attack is fractionally looser, about 1cm?, never noticed till i put them together now. i’m about 30″ jeans btw. (Endura always had to be done up tight, the Altura fit so well (read: 70s porn star) i can ride with them undone and they stay up 🙂
so if medium Attack is slightly big for you, medium semi-dry should be ideal – assuming they haven’t changed sizing!
hope they carry on making them, the best i’ve found. agree with OP i like my knees covered always.
edit2:
if anyone has massive Chris Hoy thighs don’t get Alturas, you will look ridiculous and probably not be able to move.