Until you rent a 5dmk4 you will never know how much different it is compared to your previously owned 5dmk3 Colour isn't the drastic difference between the 5d3 and 5d4. Sharpness and render is different between the two Canon bodies. I would pick my 5dmk4 over my 5dmk3 in many cases.
The Sony A7iii render is completely different to Fuji or Canon. The 3d pop factor in Sony is almost like you've hit an image with aggressive contrast/clarity even in RAW file form compared to Canon and especially Fuji. This can be both taken in a negative way or positive depending on your image you want to create. Crafty post processing is required.
Now that I've been using the new Sony body for well over a month I've observed many different things with Sony compared to Canon and Fuji.
Fuji is still the easy "eye candy" maker with little effort in post processing. Sony for me has been an incredibly challenging journey with AGGRESSIVE greens, reds and orange for skin tones. The sharpness from the Sony sensor is almost too sharp with my adapted canon glass. So far Sony makes my Canon and Fuji softer in shadow transitions and overall micro contrast. I'm reducing Sony's raw contrast, clarity and even playing with dehaze in LR classic CC.
Greens in some lighting is punch you in the face green. I'm manipulating my post processing with a bunch of Xrite passport presets I'm creating. Also lowering the "green" path.
Over a month of playing with my own Sony files I'll say there is NO doubt a huge difference in how the electronics running the Cmos sensor rendering different.
Google sony images and you'll see a lot more contrasty images. Definitely the micro contrast is piercing sharp almost like hitting an image with aggressive unsharp mask in Photoshop. This is where my observation sees piercing sharpness and aggressive colours when you would imagine the photog depicting a subtle sensual image. I find contradiction in how Sony images looks sometimes in how Sony Raw files are NOT easy to make the eye candy fuji produces with NO effort.
Sony files I'm finding I have to use the slider to reduce contrast/clarity. Strangest thing I've ever had to do for human subjects.