Hi Camel,
Firstly welcome to the HUBB,
For a quick trip to North Africa where you are not venturing too far from the dealer network and an LR Testbook the D3 is fine.
They are refined on road and will eat up those autoroute clicks to/from North Africa.
The D3 is a very capable vehicle off road, I would be going for the TDV6 auto, in sand, the autobox and terrain response make a great combination.
However, for my money if your driving a 110, then you already have one of the best vehicles for overlanding and the 110 will go places that the D3 will struggle because of its 700 kg heavier kerb weight.
There will also always be the worry of a sensor failure and the possibility of ending up in 'crawl home' mode when you in the middle of a dune field.
Id think about spending some of that considerable D3 cost on making the 110 better, installing D2 high range gears, beter soundproofing, better seats, engine enhancements etc and end up with a great allrounder that you can rely on further off the beaten track.
Also, before you spend your hard earned on a D3 - try a newer Tdci Defender with a 6 speed box- still a higher tech CRD, but the few sensors the Tdci has are generally a lot less prone to off road damage and theres a lot less electrical gubbins to go wrong on the rest of the truck.
That may be a better compromise.
You can also put a brew or a bottle of

on the wing without it sliding off.....