I'm trying to decide between a 400 and 520 EXC for here in Colorado (my old bike was a 300 EXC). Reviews at sea level seem to say the 520 has too much engine for where I'll spend plenty of time (very tight sections, roots, big rocks, slow-going). But I've also heard 3% power loss per thousand feet, so I wondered whether a 520 at 8 or 9 thousand feet is just about the same as a 400 at sea level (and so would be just right). Comments, ideas, experiences? TIA, Steve Dz.