Con's = Potentially worse gas milage (usually not due to the steeper gears) and less high end acceleration. Traction becomes a big issue with street tires.
however, the gas milage definately gets worse, because you will drive like a dumbass lol. the gears dont really hurt milage at all on the highway.. the drive to a local track used to cost me 30 bucks, now its 34-35 ish.. so really its not that much worse.. but having the pedal on the carpet more often definately hurts the milage...
and with my 96 auto i have huge traction issues.. you should have the same tires, but more power and a 5 spd.. so you do the math..