My research is easy when they have a "Technical Data - Ride Manufacturers Information Plate" sign like this!
When detailing a ride on my website, I don't normally list a roller coaster's top speed. I do this for various reasons. First off, there are so many factors that change a ride's speed. A fully loaded train on a warm day with light winds will be extremely fast, yet an empty train, or a cold day, or even strong headwinds, might be enough to literally stop the train in its tracks. In fact, most manufacturers specify a minimum air temperature and maximum wind speed for a coaster's operation. Secondly, a lot of parks tend to exaggerate a roller coaster's speed. This may be due to the difficulties in accurately measuring a train's velocity, or it may be simply to market the ride as a faster ride. A park's public relations department might throw on a few extra miles per hour when hyping a ride, and it is nearly impossible to prove them wrong.