I'd recommend playing HR on harder hards to easy insanes (AR8+ OD6+ CS4+) at that level. If you can't easily maintain 90%+ accuracy and find yourself mashing, then it is too hard. The higher the accuracy you can maintain on the song without it being too boringly easy for you, then the better it is for training accuracy. If you can find some harder stuff with complex patterns, then that will help you get used to reading AR9.8+. Also, make sure to play some AR9 or lower stuff every now and then so you don't get too used to AR9.8+ to the point where you can't read lower AR anymore.