few n00b Question(s)

I work for an international aviation service company that does international trip planning (including flightplanning/etc) for private/charter operators. This is mostly bizjets. Our rule of thumb around the office is just what Chris mentioned. Even though I sometimes think it's a little conservative (low altitude), we typically file cruise levels that represent 1000' for every 10nm of distance between the cities. Globally, it tends to yield the highest average altitude available to still account for SIDs/STARs and ATC restrictions. So a 250nm flight would be FL250. And most of our customers fly bizjets - some of the fastest climbers in civil aviation! Of course, if you're familiar with your citypairs, ATC, procedures, and airplane performance, you can adjust that to something more specific/achievable. (For example, KIAH-KDFW is typically filed by the airlines between FL240 and FL300, but is only 213nm.) Ours is just a rule of thumb we apply to any citypair you can imagine, and almost any modern transport-category passenger jet you can imagine. -Tony