My point is the tropopause is extremely variable and generally reacts to the polar and sub-tropical jet stream. You'll note that over New Mexico the tropopause is estimated at FL290 because the jet stream takes a crazy dip south, then back up over the great lakes, while way north in the province of BC and Ontario it resides at FL340. Its all in the link I gave you several posts back, good stuff.
Aside from that we are talking about high-altitude aerodynamics of commercial (long-haul, doesn't matter, more importantly swept wing aircraft) aircraft. As you near the tropopause the temperature ceases to decrease, and may even warm. Therefore, as a jet climbs through this extremely thin layer of atmosphere, it will suffer in performance due to temp stabilization, or temp increase, while air density continues to fall. In addition, there will most likely be apparent some form of turbulence as the jet transitions out of the jet stream into calmer air. Turbulence at or near a jets' max service ceiling is dangerous due to the coffin corner issue, which is the zone where mach and stall get dangerously close together.
Aside from loss of aerodynamic performance, you also increase fuel burn making it pointless.