Maybe low to mid XXX on Gatwick. Probably will be a hard sell, as it doesn't seem like an extension that an airport business would use.
Exemplify.org sold in 2013 for $3,455. So, the .xyz extension may have some value. I would BIN it competitively to sell. Maybe in the low X,XXX range. You can always drop the price later (or even auction it) if you don't see interest.
I don't think that there is much value in 4L .xyz names. Even some 3L combinations are still a hard sell.