I'm looking at taller 6-speed gearing for an application with a car that's also lighter and more powerful than a stock STi... I've found a 'high speed' gearset (which I think is from the Forester?). I'm not sure if it's as strong or the difference would be noticeable enough?

http://www.rallispec.com/gea_syn_rstf145.html

1st - 3.636 2nd - 2.375 3rd - 1.761 4th - 1.346 5th - 0.971 6th - 0.756 (2005 STi ratios)
1st - 3.636 2nd - 2.235 3rd - 1.521 4th - 1.137 5th - 0.891 6th - 0.707 (HighSpeed ratios)
1st - 0.000 2nd - 0.140 3rd - 0.240 4th - 0.209 5th - 0.080 6th - 0.049 difference
1st 0.00% 2nd 6.26% 3rd 15.78% 4th 18.18% 5th 8.98% 6th 6.93% percentage

Anyways, it might be something to look at-