Titleist claims that the swing speed doesn't actually affect the performance. Also, the two golf balls are very similar with the minor differences being that the ProV1 is slightly softer with more spin. The ProV1x has less spin off the tee which unfortunately means slightly less greenside spin as well. As long as you are good with your wedges the ProV1x will give you more distance. That's what i play anyway. Test them both and see if you find and more subtle differences. Hope this helps.

Exactly what he said.  Swing speed is not as a big as a factor as some people bring it to be.  ProV1 is softer with the more spin, and the ProV1x is bit harder making it longer.  This is why I believe most pros play the ProV1x, because they already have enough spin that they can sacrifice some for distance.

I got the 2013's and found the new x's to be closer to the 2012 pro v's in softness. I was testing them side by side. I did still get more spin with the 2012 pro v's than the 2013 x's but the new x's hit and stop on long approach shots and spun back nicely on shorter ones. Slightly better than the 2012 x’s did for me, with a slightly softer feel. Very durable and basically the best ball I have ever hit.