If I was starting again from scratch I wouldn't rule out buying the 658 instead of the 800, as a new bike purchase.
Because in trying to build one for 2-up dirt touring I have had to replace the suspension anyway, and the 658 is a fair bit cheaper than the F800 anyway. It has a better low end and mid range, and is better on fuel.
Basically, the F650GS is cheaper by a margin large enough (well, they are here) to pay for all the suspension upgrades and other mods you want to make. Even factoring in spoked wheels.
For the same money as a F800, you'd have a fully set up 658. Same engine, same frame, same electronics, etc etc. With a spare set of road wheels.
Just a thought.