Piano Forum

The K. 517 is not fast enough to constitute 'improving speed in scales.'  If you can't already play an isolated scale at that tempo, then you shouldn't be trying to play that piece at all.  I think you should just pick pieces that you like, and continue practicing your scales like normal; there are lots of little rhythmic/dynamic games you can play with your scales that help you build up more confidence and speed, prolly you already know about them.  Of course there are also 2/3/4-finger exercises related to scales as well, especially thumb under/over stuff.

How about just learning some little passages from pieces that you love?  That seems better.  Like, learn the very end of the Chopin Ballade 1, with those parallel chromatics.  Kind of notorious for tripping up people just starting with that level of rep.  Many other examples like that, like from the Pas de Deux in the Pletnev Nutcracker, or maybe an extract from the Waldstein 3rd movement.