well, i spoke to a performance dept. mechanic at a dealership and he said, those numbers are put in the manual to match the fuel economy figures, but in fact, you should NOT drive like that. eventually you'll have enough carbon build up in there to significantly decrease your performance.

having already put 1600 miles on my X all over the state of Maine, i would say fuel economy concerns is the last thing on mind, when deciding which gear to use. sometimes you just can't use a higher gear because you will simply lose traction in a turn. there plenty of single lane roads here, where with a speed limit of 55 you end up averaging 40 MPH because of the turns and uneven pavement. i'm not even going to mention the multitude of various size hills...

judging from how the throttle responds in the lower range RPM in the first 3 gears(in second you start feeling major torque at 1200), driving under 2000 RPM isn't too stressing for the engine, unless you floor it and shift instantly, i guess...