When my fingers hurt after too much time on the keyboard, I stop typing, take a break, and return to typing slower than my capacity. That helps my fingers to return to their flow state.

I'm judging by your performance improvement and number of tests completed that you are using other methods to improve. You are roughly where I would like to be in terms of speed, and seem to have started off here just below where I am now, so your advice would be invaluable. Thanks.