its been stock for about 6 months now, and its time too spend some money on her. what do you guys think is the best 1st mod for my cobra. probaly about 5-600 too work with. currently all my car has is flows, K&N filter, and exterior upgrades, thats it. what i had in mind was a midpipe,catback,or 4.10 gears. which would be best too start with?