Slipping in 5th is the first sign your clutch is going. It's under the most load in the higher gear and thats why it starts slipping in 5th first. If you drive on it long enough, you'll notice it to start to slip everytime you accelerate hard in any gear.
I would suggest, that if you are performance minded, to do your flywheel at the same time as a clutch, or at least have it resurfaced.
Exedy makes the clutches for STi so you can't go wrong there. I also like ACT quite a bit as well.
If you'd like you can give me an email and I can put toghether some pricing for you on a couple different options.
As for pullies, to give you an example, I run a fidanza 9.5lb flywheel and our TB Racing 1lb crank pulley and I have no problems with stalling or anything of the sort. With the extra torque your car has over mine downlow, you should be even better off to go light.
To solve the lights going dim, we have a lightweight pulley that is stock diameter. So you get no accessory power loss, and you use oem belts.
You'll get the increased throttle response of a pulley kit, but not all the side effects.
let me know if you have any questions on any of this
Brad
TB Racing