The engineers that develop the technologies incorporate all the layers of the ball to create the characteristics.  Core hardness, in my limited knowledge would really only be a major factor in a 2 piece ball.  Thinking of the 2 x 15 distance balls for 24.99.

You would really need to test both balls on course to tell the difference.  Your first decision point should be from your shots to the green, and how well the ball responds to your partial and full swing.  If you are still undecided, then compare on your metals.  I'm no pro at ball speed, but the v1x gives me a boost on distance with a shallower descent with more roll out on driver/fairway shots.  For that matter, so does the NXT Tour (not so much the -S - my not favorite yellow option).  It really comes down to your swing and how you contact the ball.  You can't really judge off of charts, diagrams or online ball matching applications.

If you can catch the Titleist rep on a ball fitting, you can have them check your swing to compare balls with a Trackman.

Hi David,  I spoke with our lead Golf Ball Fitter on our West coast team and here is his explanation.  The ProV1x has a higher initial launch angle than the ProV1 due to its dimple pattern.  The biggest difference between the Pro V1 and the Pro V1x is spin on full shots.  The Pro V1 spins more. 

Core hardness does play into distance, but not as much as some think.  The Pro V1x has a firmer outer core surrounding a softer inner core, which produces lower spin on full shots compared to the Pro V1's soft single core.   Both balls are long, but by optimizing spin and launch conditions, one will go slightly further than the other, depending on player.  .   

My playing partner and I play different Titleist balls.  I play the Prov1 and he plays the Prov1x.  He is a 2 handicap and I am a 10.  We hit the ball about the same off the tee, but he is about a half a club longer than me with his irons.  He hits the ball lower than I do because I do like to tee it high and let it fly.  I did forget to mention that I am 68 and he is ten years younger and I have only been playing since 1985.  A late bloomer.  I was fitted for the Prov1 because I am a picker and need the spin around the greens.  My partner is a digger and can spin it off the green.   I used to play the Prov1x until I was fitted based on my game.  Great golf ball, if you ask me.......just ordered my 3+1 offer....thanks Titleist....