Can anyone explain to me how helpful IS is compared to non IS, all my lenses are non IS and with zoom (300mm)I cant seem to shoot below 1/125 shutter at f5.6. With IS do you think Id be able to go as low as lets say 1/60 or would it be slightly helpful maybe at like 1/90 over 1/125. im just curious if its worth the extra $150 or $200 for an IS lens over a non IS, what Id really like would be an f2.8 75-300 but I cant find any under a grand (anyone know where theyre cheaper?)