Basically a really large EF4 tornado, however these speeds are only found in the eyewall so it's not as bad as it sounds.
No, this is like a tornado 100 miles in diameter, moving at a walking pace.
You're right to note that the winds actually aren't the biggest danger. That prize goes to the ocean surge. Water is a little denser than air, so it tends to require less movement to do a lot more damage. But don't discount what winds like that can do.
Here's one projection, showing Irma impacting south Florida pretty hard. Luckily for the USA, in this model it drags itself along the length of Cuba, which impedes its wind speeds significantly. But I can tell you from experience that sustained winds in excess of 60 knots are not to be trifled with. They'll knock down a lot of walls, trees, power lines and the like, as well as breaking a shitload of windows. The storm surge looks to be pretty heavy for Miami, too, so even if the winds don't knock it about, that doesn't mean it's scot free.
I've been through a Category 5 cyclone with similar winds. Let me assure you, it's not a pleasant experience. We lost eight out of eleven state of the art cyclone shutters around the house before it let up.