An author for the Washington Post did some research on Fangraphs and came up a list of the hardest throwing starters. Josh Johnson is number four.
4. Josh Johnson, Marlins. 94.9 mph. After Tommy John elbow surgery cost him much of the previous two seasons, Johnson is back with a vengence this year. He's throwing 3 mph harder than he did in 2006, his last healthy season, and 1.4 mph harder than he did last year when he returned from surgery.
Not sure of the methodology but I'm guessing he just used the average fast ball mph for the survey. Which would be the normal way to do it. But whatever, Josh Johnson gets some press.