My buddy is 6'1", and he was perfectly fine driving that Xterra. In fact, he wouldn't even put the seat all the way back! I guess he just preferred that seating position. I'm 6'3", and a bit long in the legs, so in most cars, I put the seat back as far as it will go.
Still, we went on a few road trips with that rig, the longest being from the DC area out to Cedar Point in Ohio, about 420 miles away. My legs would start feeling a bit cramped after awhile, but it was doable. My guess is that it's probably just fine for about 90% of the drivers out there.
As for fuel economy, I didn't think it was bad, considering the weight, power, and the fact that it had 4WD. He probably averaged around 17.5 mpg during the span he had it. I told him to always keep track of his fuel fill ups, and calculate the mileage so that he'd notice right away if it seemed to drop off unexpectedly. I'd say about the worst he'd get was around 15.5, in winter weather and short-trip driving. It would get about 22 out on a good highway run, if you kept your foot out of it. We took it on a few road trips, and while he was good at that, whenever I'd drive it, it seemed like it liked to creep up to 80+ with little strain.