I've done a lot of ridiculous things with my EX in the time I've owned it. When I was younger, I really pushed the limits on the thing in terms of speed. Fastest I ever got the speedo to indicate on a dead flat true country mile in the middle of nowhere was 124. Fastest I ever got period was downhill at 128. I know from running by the various speed traps over the years (the ones with the digital readout of your speed) that those numbers are not accurate. Speedometer error would put my actual speed on the flat under 120 by several points.
I must say, the bike in stock form is terrifying at those speeds. Again, years ago when I wasn't as mature a rider, I pushed the thing at around 90 through a long swooping left hander over the double yellow to pass a hot shot R6 rider who wasn't as comfortable or daring (or stupid really) on his bike as I was. I hit some small bumps in the road going through that corner and it suddenly felt like I was riding a wet noodle held together by rubber bands. Thing almost put me into the side of the cliff. Haven't made that mistake since.
The fastest I would say the EX is comfortable with on the straights is 100. On the twisty roads, I wouldn't recommend anything much above 60. Below that, it's quite an exciting bike around the corners and is still a blast even after all these miles of riding it.
If anyone currently on a 500 really wants to get going fast, here's my recommendation. First, master the EX. On the street, it takes a good long while. Once you become truly comfortable with dragging the lower fairing through a corner, then go to something more advanced. I personally chose a Ducati 900SS. Unlike the EX, this is designed to easily hit speeds well over 100 AND handle. I've dragged the pipes on it around corners at 80-90mph and it feels right home. The higher the speeds, the better it handles, which is the reverse of the EX. It's a combination of suspension and frame geometry.
However, I've yet to ride a bike which is more nimble and easy to maneuver in traffic, city streets and sharp corners as the EX. Despite my love for my speed demon, it makes a terrible commuter. The EX will always remain my trusty daily steed.