in your opinion which would be the best lens for concerts? tamron 17-50mm f/2.8 or something like a 28 or 30 f/1.4? i need it to be fast, but the reason i want the 17-50 would be the versatility. i need the lens to also be wider and more easily used if i am 2 feet away from the stage. considering which one to buy. thanks for your help!