Hi Jeff - 

The D3 will spin approximately 200-300 rpm less than the D2 (everything being equal).

Hi Nick. at what club head speed was this measured at. and what is the range as it goes up and down the chart of swing speeds and angles.

Hi John - 

Computer and robot testing for drivers are typically run at 110 MPH swing speed (roughly 163 ball speed), with a square face at impact and a slight upswing.  We perform player testing, which varies in many regards.  This testing incorporates ball speeds between 140-175.  Attack angles will vary depending on the player but the D3 will still spin less.  How much so, can only be determined by a proper fitting.

Hope this helps...