Hi Mike,

If your wanting to do a lot of the off the beaten path stuff as well as travel long distances then a 650 class bike would be the best compromise...

The 1200 GS is basically a streetbike that you can ride on gravel, great for eating up miles on easy terrain but tiring and slow in the rough going... After a while you may shun riding in to some prime spots because of the difficulty and effort it takes getting a hefty bike in there... Also if you drop the thing the effort required in getting it back up will get old pretty quick...

The DR 400 is a great machine which performs well in a rough terrain role, but for long days and lots of distance it will for sure be lacking in the comfort department... The bike is reasonably light so you can pick it up even with full luggage aboard which is a plus... The stock seat should be replaced with something wider and more cushy and the fuel tank is small so that should be addressed... The downfall is that the engine will be more stressed at freeway speeds and running an engine closer to peak capacity for hrs on end becomes tiring in a hurry...

Looking at a 650, the KLR fills the role quite nicely... Right off the get go the bike is set up well enough that you could go with it... It has less dirt ability than the 400 but much more than the 1200 and also does pretty good on the pavement... The engine runs pretty comfy at all posted speeds so unless you are into blitzing it should do well for long distance...
The DR 650 may even be a better choice as it does better in the off road and is lighter than the KLR but requires much more setup to be travel ready...