If you comb the Internet for information on Venus, most sites will tell you that the average wind speeds for Venus's top layer of clouds are 300-400 kilometers per hour (about 180-250 miles per hour). The jet-stream on the earth travels at only about 225 kilometers per hour (140 miles per hour). Keep in mind that the Earth is also spinning much faster then Venus. The Earth spins once on its axis every 23.9 hours; Venus takes 5832.5 hours (about 243 days). This super-rotation of Venus's atmosphere is still not understood.
I am currently working with a group of scientists trying to better understand these winds. The really cool thing about all of these unknowns is that there are scientists working on understanding them. Finding out what drives Venus's atmosphere will probably give us a much better understanding of our own atmosphere as well.
Image credit- NASA