W1AW Code Practice Files with the speed 25, 30, 35 and 40 wpm are currently in my iPod.
I do not perfectly copy even at 25 wpm, but recently I began to enjoy listening to 40 wpm files. While I always stumble in the middle with the longer words containing enough number of letters to overflow my small brain, I found that shorter words are really easy to understand, perhaps easier than at slower speeds, because such words jump directly into my mind without intentional efforts.
When I came back into ham radio after many years of inactivity and seriously wished, for the first time in my life, to be a good CW operator, my primary concern was if I could keep my interest and enthusiasm until I break through the barriers that must be awaiting for me somewhere along in the course.
Of course, there should be many barriers each with different nature at different stages, but I may have broken the first few ones, because now I do enjoy listening to 40 wpm.