Just one thought for the OP - all other considerations aside, remember that Vx is best ANGLE of climb, whereas Vy is best RATE (by definition).
Therefore Vy will get you away from the ground faster - if not there's something odd going on. Possibly it's an illusion that the climb lags? 1 minute after takeoff you'll be closer to the ground with Vx but you'll be closer to your lift off point - if that matters (e.g. when there are obstacles..)
Last edited by Mark1234; 25th Aug 2012 at 22:02.