I hit the same wall around Level 22 and basically gave up for a few weeks and had to come back and clear out over 1400 reviews in order to pick up where I left off. Original post on that here
100/500 was what I settled on to keep my daily numbers manageable. Anything from 80-130 daily reviews is manageable given the time I have to spend on WK, so that’s how I managed to keep my sanity intact. 