I can't really help but I can say this. I had the JV-1010 and an XV-2020. Which I guess is a fair comparison between the JV sounds and the XV sounds, being that both are 1/2 unit, limited sound modules. I will say without a doubt, the XV-2020 was better sounding. Now it may have been the effects, I don't know.
You obviously know comparing the XV-5050 to the JV-1010 in all other aspects besides the sound, the 5050 has way more features than the 1010, but you're just asking about the sounds quality.
Based on my experience with the two synths I had, the XV sounded better than the JV.
I think the XV has different wave forms and therefore different patches, but I do know that at least some of the wave forms from JV are in the XV. For example the Augermentive (B3 patch) in the XV-2020 was identical sounding to the Augermentive patch on my XP-80 (which uses the very same sound set as the JV-1010) and there was a pad in the user banks called "Gluey Pad", that I loved, was identical in both the JV and XV. But there were many wave forms in the XV not found in the JV.
Have you posted this question to Roland themselves? I'd be interested in knowing the truth.
Best Wishes
Bob