My average backhands are ~90mph, so I have crossed plenty of 100mph backhands, nothing impressive.
Simon vs. Isner should be interesting. It'll all depend on how well Isner can play in the tiebreaks and it's all about Isner's serve. I'll give the edge to Isner, just because he has some confidence these days and the dude with the serve always has the edge. Not to mention Simon hasn't scaled the heights he once did, wether it's mental or physical I have no idea.
And Bab you were right, people tend to overlook Simon for the "three musketeers" but I respect him ten times more than Gasquet and Monfils, and Tsonga has only recently started showing a little stability.