Amazing ~! Awful lot of work , though... Never did multiple images and layered them. Too old school = just use the aperture and critical focus.
Really nice feature of the Rollei SL66 > had a dropping front bed for the lens > would do almost exactly what the required steps you have taken ~~ in one exposure.
Scheimpflug principle http://en.wikipedia.org/wiki/Scheimpflug_principle
With film :: you simple expose for the lows /mids and then process the film to hold your sky value ...Even this bright of situation = you could bring that sky down with the Zone system.
Digitally :: Expose the first image :: focus 2/3's in (roughly) at ISO 100 > 500 @ 22 > 24mm ++++ second image at about 125 @ 22 >>>BLEND
Yes, you can do that.
I use a 4x5 camera too, but:
- the image quality I get from stitching is clearly superior,
- the bulk of the equipment in the field is a lot less,
- autonomy is pretty much infinite while film sheets strongly limit the number of images that can be captured,
- DoF stacking is more generic in that it can render a scene sharply for any type of subject, not just those sitting in a plane,
- I find stitching to be fun!
But I am not trying to convince anyone that this is the way to go. It is just one tool in a tool kit.
Cheers,
Bernard