I'm comming in on this one really late. But seriously for the best cost/power ratio. Lose the weight. 98 legacy gt's are pigs. I know because I have a 97 legacy gt. I'm not 100% sure my numbers are correct since I did figure this out while drinking. But for every 11lbs removed from the car is equivilant to a 1hp gain. Now if you're having troubles figuring out to remove then you need to get creative. Like droping in a hawker dry cell battery, removing the spare and jack and replacing with fix a flat. If you really want to get into it. Remove all the sound dampening and use rubberized undercoating to dampen the interior. Still dampens and weighs much less. Unfortunatly AWD weighs a lot. But if you can lighten the car from other areas you have the best of both worlds.