Go to a club fitter and get properly fit for your swing speed and swing type. Loft on the driver and the shaft will correct your concerns. The D2, D3, D4 come down to personal preference. Do you like to work the ball or just hit it straight ? Do you like the setup of the head ? Launch angle, angle of attack, back spin, etc., can all be set through a proper fitting.

Was fit for my current driver. My question is how much of a reduction in spin could one expect with the D4.

I am interested to hear that answer myself. I hit it straight (67% fairway, 90%+ playable), have a decent swing, 92-94 mph ave., play a 10.5 D2 which is presently set down -75*. I feel like my launch angle is good. Ball usually takes off on a mid trajectory, but rather than continue that nice boring flight, very often continues to rise as if it found extra lift or a head wind, then drops out of the sky and virtually stops, will little to no roll. Even the guys on the tee will say, "big drive," then we get out there and I'm barely to where they are. I used to be the longest in my group. Now it is rare to be longest. I play a regular flex Aldila Rogue Black 60. I was fit at a big box store, but I am not convinced this is the right shaft for me. Or maybe not even the right driver. I previous played a 913 D2 with a VTS Silver and had similar issues. I had a 910 D2 stock off the shelf before that and think I hit it better, though my swing is much better now. Doesn't make sense. I want to play Titleist. I guess another fitting will be in order, but I would like to have an idea beforehand, what shafts and/or heads might be good to try first.