I probably should not be commenting. I'm playing the alberti base in C major Hob. XVI:1 -- much, much simplier piece

. The score is marked allegro and the editor suggests a speed circa 132 to the crochet.
At times, I think this is impossible, but I've made significant progress on getting up to speed and keeping it neat.
Assuming that I want to play at 132 proper, I should be practicing at about 150, so here are a few things that seem to work.
1. Definately forarm rotation, nothing else will do.
2. Make sure your wrist is alighted to the keyboard, move your trunk if necessary. I tried doing an Alberti bass (c chord say), at C3, C4 and C5 without moving my trunk and it get's increasingly difficult to play with my wrist misaligned.
3. Pulse the down beat. This is to help you keep rhythm. At that speed it is difficult to keep rhythm. I find the irragularites creep in because I loose rhythm. Although the simplest way is to use the down beat, e.g. beats 1 and 3 in common time , I sometimes try something more suitable to the passage.
4. Make sure you can hear the passage in your head at speed. I find that a lot of the time I can't play it because my brain isn't used to the rhythm at that tempo in the first place. So I get brain used to hearing the passage at that tempo by listening to a recording or playing small passages fast.
5. Practice hands separate fast, hands together slow.
6. Practice short sections - one/two beats (crochets) at a extremely fast speed. Stop immediately after and make sure there is no tention. It is much easier to keep rhythm and use the correct technique in this way. I think of it this way -- If you can play one beat, you can play two and if you can do two, three is easy as well... Keep increasing the number, beat by beat, paying attention to chord changes.
7. I find that when I do play up to speed with my fingers without tension., I feel as if I am touching the keys and not pressing them.
8. Practice on an easier sonata. E.g. the one I'm playing! I find that the simpler it is, the more difficult it is to get a good honest sound. You don't have to worry about other technical issues. Only about producing a good sound. Somehow for easy pieces, everything sounds bare and any inaccuracies stick out like a sore thumb. Also, making it interesting enough for a performance by having a good lyrical tone and good contrast at speed with neatness and accuracy is no easy task.
Hope this helps.
al.