Most Nikons have a lot less noise than Canons at base ISO. DP Review calls it "ISO invariance". In real world shooting you can get away with underexposing a Nikon (I'm talking about raw photos, not video), whereas you have to expose to the right with a Canon to achieve the best results (raw photo and raw video). The 5D MK4 isn't as clean as a D750 or D810 at base ISO, but it's a lot cleaner than a 5D MK3. Interestingly, although Nikon uses a lot of Sony sensors, Sony cameras don't like to be underexposed, especially if you're shooting sLog.
From my experience shooting with a bunch of cameras, DXOmark raw dynamic range results appear to be accurate. Noise measurements aren't as accurate a guide for video shooters because they don't take into account problematic things like highly compressed codecs, fixed pattern noise, or blue splotches (A7s).
Doing your own tests and finding a sensor's sweet spot is crucial to getting the highest dynamic range and least noise out of any camera. Proper post processing of raw files is equally important. Every camera has some quirks that lab tests don't pick up on.