I've never been to the Mihagino Batting Center because they are located a little farther away than I'm willing to travel just to hit a few balls (and especially because the Jinguu Batting Dome is just a few minutes walk away from me), but I just read some news about how they have temporarily upped the speed on the 180 km/h machine to 200 km/h (or about 125 mph). The fastest machine I've ever faced was 130 km/h, which is the max speed at the cages near where I live.
The 200 km/h machine will only be around for a limited time though (until 11/4). I only I had some time, I'd take my butt down there and take the challenge.
Below are the links to the Mihagino Batting Center and Jinguu Batting Dome for those interested. They are in Japanese.