In a heartbeat... Not to start a holy war between the two but a lot a review sites concede that the nikon bests the 5d3 from ISO 50-800... It also has a pop up flash, clean HDMI out, more mega pixels. Everything else from ISO 800 onwards, to AF, HDR, video (canon pounds the crap out of the D800 here), battery, battery life, ergonomics, handling, custom settings, on and on and on... If i was a landscape or MF shooter, then I may be tempted, and only tempted, in the D800, but in the end, it's not enough of a IQ edge below 800 to get worried about. But for me, how I shoot, and what my clients needs and wants are, it is what it is...