I enjoy Sonny's Mazurka too!
I used to play it more up tempo, but lately I've been enjoying it at a little slower speed. I don't know what the typical tempo is for a Mazurka, but I heard some of them played a break-neck speed, and some played as a more stately dance. To me, Sonny's Mazurka has a dream-like quality to it, I think that's why I've enjoyed a little slower.
I use the fiddler's fake book quite a bit, and have found it to be a really valuable resource. It doesn't have everything, but it will keep you busy for a couple of years! Hardiman