If not mistaken a 2.5 STi will have "forester ratios" and will have longer gearing than an earlier UK 6 speed.
You need to get the gearbox code to confirm what its out of but mine is:
DW-TY856WG7KA
and has the following ratio's:
1: 3.636
2: 2.235
3: 1.521
4: 1.137
5: 0.891
6: 0.707
Reverse: 3.545
Final Drive: 3.900
Which gives
these speeds (on my tyre sizes)