My experience is from 56 and lighter is quite irritating to play chords on because you have to play very light to avoid strings toughing the frets because they become really wobbly. %9 and thicker is awesome because they dont have that problem and for solo playing tehy dont soom hard just a nice tension altogether
I use a 54 for a B on a 25.5", and it's just fine to me. I have a 56 right now because I wanted to try heavier strings, and I can barely feel the difference on the low strings, but I can't bend as well on the high strings because of the stiffer tension. 9-54 sounds like a good fit for a 7 string at 25.5", from my point of view.