I need to get a 2.8 lens. Considering both lens, which one should I get? Is the 70-200 really worth the money? The problem is, I do have the money to get the 70-200mm but if I get that lens... I will not be able to get the 17-55. Should I get the 70-200 and forget about the 17-55 for now? What should I do? Thanks for your input.