I had D606 on both the DR and TE. Excellent on and off road, including wet tar.
Yes, if you gas it continuously you might not see more than 2500 km on a rear.
They say the CO2 lasts longer, so it should be a harder compound.
I had a CO2 on the 500 for the Kaokoland trip, and not much left at the end of it, which was hardly 2k. It has a D606 on now.
Any tyre will wear when being abused on gravel, specifically hard gravel, which will be like sand paper on the tyre.
I would focus on affordability and performance in the terrain that you ride.
Puncture resistance on both was excellent with HD tubes.
Yes, pictures please Tony.

Sent from my FIG-LX1 using Tapatalk