I use a D750 at work and shoot with a 6D at home (work and personal stuff). At ISO 100 the Nikon does have noticeably more exposure latitude but as ISO increases, any advantage disappears quickly.
Frankly, despite having read a little about it in the past, I was surprised to see for myself how quickly noise creeps into the Nikon files. ISO 200 is indistinguishable from 100 on my 6D and I use it often without giving it any thought of harming the files at all. 400 is very, very, close. On the Nikon I can see the difference between 100 and 200 with just minor shadow pushing.
I regularly shoot the 6D at 800, 1600 and 3200, I don't have a lot of opportunity to do so on the Nikon but the files I have shot that high are no better, probably worse at the higher end than the Canon. What I have noticed is that the colors and DR suffer badly with the Nikon while the Canon quality does not fall off nearly as fast.
So if you only shoot at or below ISO 200 you will see an improvement in image quality. If you are like the vast majority of photographers today, the better quality from the Canon files cancel out any benefit, on average. If you look around I think you will find others saying the same.
The thought of switching has never even entered my mind.
Now to get away from facts and into some speculation and opinion. The new 6D will be out later this year. The Nikon is fairly old tech, just as the original 6D. Regardless of whether you jump to Nikon or not, I would wait to see what each of their replacements look like.
PSA: The above post may contain sarcasm, reply at your own risk | Not in gear database: Auto Sears 50mm 2.0 / 3x CL-360, Nikon SB-28, SunPak auto 322 D, Minolta 20