I have found a very capable CW decoder called "Morse Expert" by the author of CW skimmer. It uses Bayesian statistics to predict what was sent when a letter is not 100% sure (the letter will be red). It even guesses whole words with a slight delay. It adapts to speed changes rapidly. I have used it with the CWOPS CWT where people routinely go more than 30 wpm. It may only be available for Android.
Gary
W9TD
Gary