I hope my input is not unwelcome. I noticed that all of the STi drivers were scrubbing speed in the corners. (This is something that I still struggle with from time to time.) You might try backing off on the entry speed so you can be on the gas sooner. The car is only going to go around a corner so fast, if you get in too fast it'll scrub the speed by sliding the front wheels sideways. If you go in under the highest speed for that corner you can get on the gas sooner. As I understand it the STi will actually oversteer a bit under power, if you can get on it early enough you should be able to do a slight power slide out and have higher straightaway speeds.

Hope that helps.