I would personally have ur tranny upgraded by level 10...they can make it handle all the torque u want. Then I'd take the 3.5 and have the heads potted, custom cams made, forged rods installed and forged pistons with a compression ratio of 10:1. This should be good for a 40hp increase if combined with exhaust and free flowing intake and 0 figment issues. Even with 10:1 cr u could still boost it with 5lbs if using good gas if u still wanted more.