I float my slim, svelte 6'3" 240 lb. frame across the back of a 2006 KLR and ride it 14 miles each way to work and back. The posted speeds on the route in mph: one mile at 25, six miles at 45, four miles at 55, two miles at 35, one mile at 30. It's pretty much billiard-table flat.
Besides my carcass the thing hauls most of the Happy-Trails.com catalog with a pair of $8 Action boaters' dry boxes from Wal-mart bolted to the pannier racks and a well-stuffed canvas bag tall enough to lean on bungeed to the seat. With a Dunlop 606 on the back and a Pirelli MT21 on the front I get a reliable 48 mpg.
The route winds considerably. Wind is ever-present at 10-15 mph and regularly exceeds 30. The 55 mph part is straight, prevailing winds are perpendicular to it.
With those dirt tires providing a generous 3/4 inch of contact patch every 2 3/4 inches I generally find conical protrusions in the upholstery upon reaching my destination when the wind is blowing. A new pair of Gripsters arrived yesterday which I hope will ameliorate that effect and boost mileage a bit.
I have ridden short hops on the interstate at 70 - 75 mph. The metal camel is certainly capable of those speeds and more but the fun quotient drops to a negative number. There is a pronounced sweet spot at 52 mph indicated.
At 7,000 miles on the clock there is no oil usage.
robintaz