So I own a Nikon D800, which I love. But I feel like it's way too heavy and big when I'm bringing it along for hiking or street photography. Since the A7R pretty much has the 36mp D800 sensor(The d800's best part, honetsly) I've started thinking about jumping ship. Anyone else here who has jumped ship from Nikon to this? My main concerns are low-light performance, focus speed and build quality. All things the D800 performs superbly at.