What performance limitations?? I didn't read anywhere where the OP said what the intended use for the motor/car was!! If he's building an all out race car, maybe the 318 isn't the hot ticket, but if he's going to enjoy the car on the street and just do a little stoplighting and hot dogging, then he will probably be perfectly happy with the gains he can make from the 318!
This is why I never post my motor builds here, too many personal opinions based on what the poster wants out of a motor, and not enough information for what the OP is expecting from his build! Geof