Jim OHaver is in fact dead on in what he said. A factor most do not take into consideration with multis is the simple fact that when changing from a single engine to two or more that are of similar total thrust to the single then there will be a substancial performance gain. This gain is caused by the reduction in propellor disc loading when going to two or more engines. A multi will always have more disc area even though the power is comparable to a single engine.

This performance gain will manifest itself in shorter T/O, faster climbs and generally better verticle performance but not neccessarily in top speed.

Reducing the propellor disc loading is what the 3D guys are in effect doing by using unusually long and flat propellors that are typical of that activity.

John