I have used X-outs one the past and have not seen any difference. Usually they have blew issues or lettering is off. 

If i remember rightly you're not allowed to use a ball marked 'X' out, 'Range' or 'Practice' in a competition. Balls marked 'X' out are likely to have some sort of imperfection, whether that's cosmetically or performance wise i'm not sure - could cover both scenarios.

I believe balls marked range or practice will perform exactly like a normal ball off the shelf, it's just been marked to encourage use only on the range. I'm sure the balls used on the range on the European Tour are marked 'Practice'.