I have used front panniers only for years on and off pavement with an equipment weight distribution front /rear of 60/40. The rear weight is carried on rack top in a dry bag stuffer. I have never weighed the distribution including the rider so I cannot speak to that in those terms.

Your front setup weight is too much when it includes a handlebar bag which I stopped using long ago due to the combined high position swing weight effect on steering. Options for removing the HB include mid frame bags and smaller top tube incidentals bags or shifting that weight to the rear saddlebag.

With your total equipment at 43# what would be the consumables weight for 4 days and where would this additional weight be placed? Such supplies could be needed on the GDR.

If I read your numbers correctly, moving 6# to the rear means 28# in panniers and 15# in the saddlebag. This still leaves weight up higher than I prefer towards the rear particularly with a long exposed seatpost on many bikes. [This may not be the case on your Americano.] My rear stuffer takes sleeping bag, pad and clothes- all higher volume but lighter equipment so having it on rack top is not a potential problem high above the center of gravity.

Raising the front pannier mounts was a good idea particularly for the GDR route conditions. I have no disc experience to add, but wheels do not tend to pop out of drop outs while under rider and equipment load unless nuts or QR are loose.

What is the widest tire that fits your Americano? If you can fit the 2.0 Marathon XR's I would do so for the GDR for your comfort and to reduce stress on the bike and wheels.

Try riding each configuration on the same terrain including non-pavement to test the feel for rider control as conditions change. This will be important for your proposed GDR ride. My setup worked very well on the GDR using 700x47 Marathon XR tires on 36 hole hubs and had no wheel problems although I am a significant clydesdale.

Good luck with your experimentation.