Gary's right: the Sony "beats" the Nikon Df by like 2/10 of an EV in color depth and dynamic range, but is easily trounced by the Nikon in the High ISO department, where the Nikon easily scores a thousand more points... (Well, the Nikon scores exactly 1,031 more points on High ISO/Low-Light performance than the Sony does, but what's a fifty percent better score among friends?) But Gary is right: the A7 scores a 90 overall, the Df an 89, the Canon 6D an 82 overall...
The thing about the Nikon is that it has the Nikon lens system dating back to 1959 behind it on the Df--it is one of the VERY few modern cams that can accept pre-Ai vintage lenses. There are 70 million+ Nikkors. Canon has the Canon EF mount system dating back to 1987 behind it. Last time I heard, Canon had sold 80 million EF mount lenses! The Sony has...the brand new Alpha mount, one of FOUR NEW SOny mounts introduced within the last decade...
But the Sony can use adapted lenses people say....yah...manual focus, with peaking, but...well, wow...so it's a lot like anything else that's fun to tinker around with, and I totally "get" the A7 as a way to use other manufacturer's lenses, because every 18 months, Sony invents a brand-new lens mount...and they put the A7 out with basically, four lenses...the A7 is a great concept, especially for an experienced worker--somebody in his 50's, like gsgary or me, a guy who loooooves cameras, and has some "other company's manual focusing" lenses to use until Sony decides to either defecate, or get off the pot orrrrrr, more likely, to abandon yet another lens mount and move onto the "next Sony mount"...lol...but srsly...FOUR lens mounts in less than a decade? C'mon Sony....
Sony doesn't know what way the wind even blows, or which way to p*ss...
You want AUTOFOCUS with that Sony A7??? What speed does the firing rate plummet to? An EVF with a 1/6 second lag on fast action? OMFG...
Jazzy...all you need to do is drive to a camera store and pick up a 6D. Handle it for 5 minutes. Then drive home and order something else.