I've owned both. I think the spec differences between the two says most of it. I find the 18x20 pattern and higher stiffness speed pro is more precise and has more pop. It is more powerful as the higher SW would suggest. Sweet spot is larger. The speed pro feels lighter yet swings faster.
The prestige pro offers a bit more stability but the speed pro stability is adequate so I find this a moot point.
All in all I find the speed pro to be more forgiving, precise, easier to control and provide more pop than the prestige pro. Just as the specs and power maps indicate.
I'm using full 4g at 52 lb on the speed pro. Highly recomend an extended demo.