@witiholi. Now you are talking.
At 25 and earning that kind of salary, it means you are in a good profession with very bright prospects. You are young and you can take risks. In that case, let career growth be your top priority. I hope by career growth, you mean growth within the organization and outside the organization, meaning you will be getting good experience in Y. What is the reputation of both organizations and title (some times this may be a factor when looking for the next job).
The salary difference is not that much. This should not therefore be a major factor for now.
Go for the one that have better career prospects (Y) work very hard (not like the average employee), try to learn as faster as you can and if situations allow, get to learn you supervisors duties, have a good relationship with them. After about two years, they should have noted your effort, if nothing is coming your way like promotions, start looking outside as you work hard but only go for something that takes you higher up.
If however you are in a career that has generally low growth prospects, go for X and find something to do in your spare time.