I use the Manfrotto Befree Advanced, it is just a matter of taste and weight.
I also shoot stationary cars
[1] [2] sometimes and only use my 50mm f/1.4 and my 70-200mm f/2.8 L IS (mk1) and I would say 90% of the time wide open.
I totally agree with this. By using the 10x magnification, you avoid the micro adjustment required by the auto-focus.
On the pictures you showed, you don't seem to use the range 35-70, as a result I second the choice of going for the 16-35 (I have never used TS lenses).
Personally I would replace the
EF 17-40 f/4 L and EF 24-105 f/4 L IS by the 16-35mm f/4 IS (as IS seems to matters to you).
Controversial opinion: I would not get the EF 24-70mm f/2.8 (I had the mk I, I found this lens to have very unreliable results for my taste).
The reason for this is that you already pretty much cover most of the range already:
- a 16-35mm will give you the 24-35 range
- the mid range you can get with your 40mm
- the long range is available via your 70-200mm.
While the loss of your 24-105mm may feel slightly annoying for portraiture, you still have the 85mm f/1.8. The fixed focal length will force you to move to frame your portraits but the f/1.8 aperture is way worth it.
All your lenses will be supported by the R5 & R6 (with the adaptor). There is no loss of Image Quality, and some says that the lenses perform better on the mirrorless bodies. Also note that you will not need the micro adjustment that you were complaining about as the focus is done by on the sensor and not by a different captor. You should also checkout the EOS R, 30Mpx and Eye autofocus for portraits.
When switching to the R5 & R6 with your current EF glass, what you will not get is the 12 FPS but only 6.9.