maxtork:
You're right that this should be checked with a rate of climb vs. airspeed chart. The problem is that there is no useful airspeed information in level flight at anything below 40 KIAS. With some of the rates of climb that are possible below 40KIAS, the angle of climb will be pretty steep, and the airflow hitting the pitot tube will not be optimum. This is before you consider the effect that sideslip will have. The sideslip is the most insidious variable in this case, because it affects the rate of climb, and unless you have a slipstring, or yaw vane, you'll never know what sideslip there is.