I recieved this camera (sony a700) as a gift for Christmas and need advice on a lens. What I will be taking pictures of is my daughters gymnastics competitions. Flash photography is a definite no. Im leaning toward a zoom lens in the 50-200mm f/2.8 variety. I'll be taking pics from the stands which depending on the venue could be as close as 25 feet or as far away as 100 ft. I read in one of these forums, though I cant find it now, some comparisons between sigma and tamron lenses. Im just wondering if anyone has any thoughts on which would be best suited for the type of photography I'll be doing. Also, any recommended initial settings would also be greatly welcomed. Thanks in advance.

JscottM