I just spent 2 hours (and about half an hour several nights ago) working with the next finer grade grit: #120 carborundum. It’s quite a different experience. The noise is higher pitched and much quieter, there is less friction, the grit takes longer to break down so each wet lasts longer, and the grit feels much finer to my fingertips when I spread it on the tool.
Since I’m close to my target focal length, I’ve switched to 1/3 diameter strokes (meaning 1″ overhang on each side of the stroke, for a total of 2″ which is 1/3 of the mirror diameter). This specific stroke will make the surfaces of the tool and mirror mate properly, meaning that they will both be perfectly spherical in shape. Although the surface of the glass rapidly become much smoother to the touch, I still have a long way to go before it’s spherical – there’s a large visible bubble between the surfaces, which clearly shows that they are only touching near the edges. Not a problem, though – I’ve used up less than a sixth of my grit, and I am quite patient!