Hello Josephine,
Just a heads up on this - whatever piano you purchase will sound different once it's in your studio. Nearly all first-time buyers complain that their just-delivered piano sounds too loud. Chances are that your studio space is smaller than the space where the piano was before. I've encountered that with students many times.
But don't be upset, because you have some control over your acoustical environment by adding (or subtracting) carpets, curtains, and sound-absorbing panels. Allow the process of experimentation with these elements to unfold over time.
You only have one piece to play? OK, but work it in different ways. For instance, with each piano test how softly the action will permit you to play. That is critical because so much expressivity is lost if the dynamic range is limited only from mezzo-piano up to mezzo-forte, but that is all. Listen to how quietly you can play before the action fails to respond.
And play the same piece, or a short passage, in every register: bass, middle, high treble, for a purpose: the differences between pianos will leap out at you immediately! Trust your ears.
Generally speaking, the longer the string length (reflected in the length of the piano), the longer the singing tone is sustained. It's no fun trying to spin out a beautiful melody when every tone immediately dies out. So, hold down keys in each register and listen to the quality, but also how quickly that tone dies away.
Best regards!