A quick answer is that the Pro V1 spins more than the Pro V1x. Check out the pages for each ball on Titleist.com

Here is some light reading for you :) 

http://www.titleist.com/golfballs/Prov1.aspx

http://www.titleist.com/golfballs/ProV1x.aspx

JUST CLICK ON GOLF BALLS AT THE TOP OF THIS PAGE AND YOU CAN GET GETAILS ON EACH TITLEIST BALL.

The Pro V1 generates more spin of the wedges and short irons. It is a little bit of a softer ball.

The Pro V1x is a little bit longer off the tee and is geared more towards a faster swinging player. However, it does not generate as much spin as the Pro V1. If you already generate plenty of spin, go with the Pro V1x to get some more distance. If you don't generate enough spin you might want to go with the Pro V1.

I play the Pro V1.

The best way to identify the difference between the Pro V1 and the Pro V1x is to try them both out.  You can take the Titleist Ball Education and Selection approach and use the advanced scorecard to quantify your experience for a more in depth evaluation process:

1) Download and Print out the scorecard from the link below.  

2) Fold along the designated dotted lines

3) Take to the golf course for on course evaluation 

4) Based on the results, determine the best ball for your game

http://media.titleist.com/images/titleist/pdfs/US/TitleistBallFitting_AdvancedScorecard.pdf

I took both out for a quick 9.  I was rolling solo and there was nobody behind me so I played both balls from tee to cup for 9.  My shots off the tee weren't noticeably longer (the 1x did roll a bit further), but where I noticed the differences was on the green and with wedge shots.

I stuck it closer, and made more putts with the Pro V (probably because they were closer).  It held the greens better and the roll out on 50/50 shots was much more predictable.  

I shot 41 with the Pro V1x and 38 with the Pro V.

In short the Pro V was better than the 1x for my game.

I must say I found your comparison of the Pro V1 and Pro V1x to be spot on.  Played Tustin Ranch golf Course in So. Orange County CA, with the Pro V1's.  I normally drive off the tee about 305 to 310 and discovered with the Pro V1's to be consistently at the 285 290 mark.  I was however extremely accurate and found myself in the fairway most of the day (knock on wood right).  The ball did tend to show more wear than I'd like, but the action on the greens was nice.  I need to head to the store and purchase some Pro V1x's next before I declare my ball of choice.  I'd certainly like to be a touch longer off the tee.  Thanks for your input.

drop both prov1 and prov1x on a hard floor.

results-

prov1 softer sound,softer balls generally are for greater spin,as it is a softer ball, has solid core with 352 dimples.more dimples generate greater spin,i guess.

while prov1x  has a harder sound when dropped, as it a harder ball is for greater distance.dual core,soft center,harder/firmer lonomeric outer layer,328 dimples.less dimples and harder ball for greater distance,I guess.

both use urethene elastomer cover.

softer balls for slower swing speeds,while harder balls for greater swing speeds,holds good for any brand of golf balls.

I prefer the prov1 over the prov1x,being a club standard player.