Remember, you'll (probably) need to install a Sorbo pad in order to adjust for AOE, so that your piston will have better longevity this time around.
And as far as springs come, it's not hard to reach 400fps as long as you have a good air-seal.
And for motors, there are a lot of options for you.
If you're willing to drop money on a REALLY great motor, you should look into the Lonex A2 motor. Probably one of the best motors out there. GREAT torque, and speed.
But again, there are more techs out there that can give you a lot of good input on these things.