I mainly shoot my kids' basketball games with a Sigma 50-150 f2.8 at 1/500 1600ISO and no flash. The results are acceptable for posting on webpages with in-camera crop and d-lighting boost, but not as sharp as I when I shoot outdoor. Will moving up to the D7100 yield better results in terms of low-light performance? BTW, I only shoot jpeg and sometime do get an unfocussed picture. Thanks.