I shudder every time this question is asked. You will get 20 recommendations all at odds with one another. Many don't even fit within your parameters. Noob + Single track + 100 miles of highway = compromise.
Being able to flatfoot is important for some just learning. If nothing else it installs some confidence when you make a mistake. Most of these single track recommendation are tall bikes. You can search the webb for the specifications of any bike. Most include wet weight and seat height.
Mine are: Honda CRF250L. Here is a comparison with a DRZ400. http://www.youtube.com/watch?v=jx1rlj2x0U8
. Tells you more than I can about the Honda.
Another choice is the the Suzuki Dr650. It is reasonably priced, physically smaller than a KLR, BMW XL and lighter than all but the XL. A low seat height that is easily lowered more. At 366lb fueled it won't meet most definition of single track bike, but maybe your definition is different.
It will easily meet your highway needs.
You can learn on that bike. Start with pavement and work into dirt mode.