OK, Rather than get involved in the debate, I will try to answer the question you have posed. First of all, I do not work for White's, but I do count one of their employees as a friend and detecting buddy. End of disclosures.
I bought a used XLT in August of 2006 and enjoyed using it a lot. I bought a Vision (now V3) about three weeks ago. Here's what I have noticed:
1--The V does WAY better on nickels than the XLT.
2--With the V I can tell the difference coins and bottle caps way better than with the XLT. Also, nails are easier to discriminate.
3--Because of the high 22.5 frequency, gold jewelry is easier. I have seen V users find gold jewelry each of the last two weeks.
4--The XLT was introduced and is largely unchanged since 1994. The V uses the very latest research and development and takes advantage of everything White's has learned in the last 15 years to make their best general-use detector yet.
5--At the club hunt today, I was the only person to find a silver ring and a silver dime. A DFX user found a silver bracelet, and a Minelab SE user found a buffalo nickel, but no one else found a silver coin but me. This in a park that has been hunted hard for years.
Those are the first 5 reasons that come to mind that I am glad I have added a Vision (V3) to my XLT.
I hope this helps. It isn't my intention to put down the other detectors mentioned above, just to relate the facts of one particular hunt on one particular day.
Best wishes in making your decision.
Mike