With mirrorless cameras offering high-resolution APS-C sensors and consecutive shooting speeds of up to 10 frames-per-second, what's left to make a $6,000 full-frame DSLR a compelling purchase, especially for amateur photographers? Low-light performance, for one -- the Canon EOS-1D X and Nikon D4 are both capable of capturing images at up to ISO 204,800, letting you snap sharp photos in even the dimmest of lighting conditions. The benefits of a top sensitivi
