The actual read/write speed that you get will depend on the card AND the camera. Some people have spent a lot of time benchmarking various combinations. Here's two lots of results:
http://www.robgalbraith.com/bins/mul...e.asp?cid=6007
http://www.hjreggel.net/cardspeed/
If you can't find the FZ50 in the database then try to pick a similar camera from the same manufacturer.