I agree with you 0nehundred80 about the cost of the diff swap compared to the value of the gas saved, I haven't done the math but it has contributed to my not doing it so far.

In terms of keeping the car, I have looked around and unless I'm missing something, there is not another relatively modern, 2 seat coupe vehicle that would be an alternative to the XF, at anywhere near the same money. Closest thing might be a 350Z, but for similar money it would have a lot more miles than the XF.

And when you compare the XF to something new, not only are the choices dwindling, but the cost of a new comparable 2 seater is amazing. Seems to me that the XF is not only probably a keeper, but a bargain.