I don't believe Clemens threw as hard as Ryan, but he was a much better pitcher. He still had a lot of movement on his fastball.
Johnson probably threw almost as hard as Ryan. At 43, he averaged 11.4 k/9. Ridiculous.
Of course, you can make a very convincing case that Clemens was the greatest pitcher of all time. And Johnson was a top 5 of all time.
Ryan was probably a top 30-40 pitcher of all time. Probably the best arm of all time though.
Verlander has taken care of his arm but it's tough to trust a 43 year old to deliver on a consistent basis.