Great question Nico. I held off having a crack at this for as long as I could, As you know. I really wanted you to have another go at it first. I hope you still get that chance.
Roxby- Lake Eyre- Maree is a good option and there are 24hr receipt possibilities in Roxby. However, while the distance via Roxby gives you slightly less gravel, I reckon the first 20ks or so out of Olympic Dam are more challenging than anything on the Oodnadatta track and as you observed, because of that It's a slower option.
I reckon with the gravel you've got to take the view that it's part of the ride and embrace it. If you ride that section with gritted teeth it's slower, less enjoyable and fatigues you more. Likewise with the Alps section. I planned 85km/h moving average on the gravel at night 90km/h in the Alps and 105 on the daytime sealed sections. In the end I was able to go comfortably faster than that, but factoring the slower speed into your calcs and understanding that you still have time in hand takes the pressure off. I calculated 22 hrs in my runsheet, it actually took a tich over 21.
If you were planning a H2H2H factoring in my extra stops for receipts and nod breaks you could probably shave that down to 20hrs, which would give you a good nap at the halfway mark and still have plenty of time in hand.
Speaking of H2H2H, I dips me lid to Karl. He suggested I have a crack at one when this was in the planning stage, but, having got to the end I couldn't think of a single motivation to turn around and head back. Maybe one day. But mentally tough and determined? You have it Sir, well done.