i currently own a 94 GT with a 5 speed and a 3.73 and some other mods. i am looking for a 99-02 cobra. my first mods will be gears and exhaust of course. i noticed that alot of cobra owners go with 4.30 or 4.56. are these surface street only cars or can/are they driven on the highway? i know the 4 valve is a much higher revving motor than a 5 liter. is this why 4.30+ is streetable? i am at 2300rpm in 5th at 75mph in my 94 and gas mileage is good. i would love to drive 4.30s around everyday but am wondering about gas mileage because i commute to work and school 25+ miles away. any response would be appreciated. thanks.