I currently shoot 95% time with my 18-300 3.5-5.6 Nikon lens on a D7100. I like the range of it, and the photos it takes, but am yearning for some better glass. Im currently looking at two lenses: --Sigma 50-150mm f/2.8 EX DC OS HSM APO or -Nikon AF-S NIKKOR 24-120mm f/4G ED VR I really do use all of the 18-300 range, shooting mostly landscapes and sunsets, with some 4 wheeling (jeep rockcrawling) thrown in. I do also find myself taking lots of handheld low light pics, and sometimes find the aperture restricting what I can do. I think I like the range of the 24-120, but wonder if I will benefit that much from a 4.0 aperture lens? Is the Sigma with 2.8 aperture that much better than 4.0? I'd appreciate any input on which lens is "better". Thanks!