I always use a softer ball when its under 50. Like NXT tour s.

I use the ProV1x and have average swing speed for an 8 handicap - about 250 off tee and 155-160 with 7 iron.  

I read on the website that the NXT Tour S was "softer" than the NXT Tour (which I read to mean less compression).  But, I was concerned that it was more spin oriented than the ProV1x.

As for other Titleist balls, my guess is that the Velocity is a hard ball and the DT is for slower swing speeds. 

Is this correct thinking?

Ball temp and layering will affect your shot more than compression.  I keep 2 balls in 2 warm pockets (pants or jacket) and rotate the ball each hole and then let it warm for 3 more.  Switching to another ball will have different characteristics on long iron/driver flight and how it performs on pitches and chips.

Not to say with more layers, you might be prone to more mishits, and a cheaper ball will be less painful to lose.  Or you switch to an optic yellow to make it easier to find and that one isn't the same ball you normally use in white.     J

I would like to thank you for the test balls you sent me in November,they go really well off the clubface gaining a good ten to twenty yards with my driver. I usually use NXT tour's but these test balls seem to bite better when hitting the green ,my  putting is much better with these as well. RAY.

Looking out my office window, I think the only ball I'll be able to use in the near future will be a snow ball!

But seriously, I haven't done any testing, but I have heard people have moved from a Pro V1 or Pro V1x to the NXT Tour and were happy with the results.  When it comes to winter golf, I just use whatever is left in my bag from the year.  I am a lot less worried about performance and more focused on enjoying some "bonus" golf.