The number you quoted is the product code number, not the stepping code,
all it tells us is that you have an XP2500 Mobile.
The stepping code is a different number altogether....the number your
interested in is marked below the number you quoted, and most likely starts
'IQYHA' or similar (which is the stepping code), followed by 4 numbers
which is the year and week number, for instance 0406 is the sixth week in
2004.
The week number is usually a better guide to overclockability than the
stepping code...As a general rule of thumb, the later the better.