I did the Tuareg Rally this year with a 640 Adventure. The bike was good, but much to heavy for the dunes for me. Maybe for an advanced rider it's ok this weight, but I was beginner in the sand, and when you have to pick it up 10-20 times ... it makes a big different to have 30 kg less.
I saw a lot of ktm 690. Some of my teammates, well all except one had this bike. all of them will come back with a 450 next year. Too heavy.
I saw a few DRZ 400 as well, I think it's a good option as well.
And there was qui a lot of Husaberg 570 and 450, the 70° engine. all were happy with it. One guy even didn't have additional tank on his.
If I had the money would buy a Husaberg 570, but the fuel tanks are so expensive.. So I think I will look for a KTM 450-520-530....
And there were a few Husqvarna and Beta 450 as well. All finished without troubles.