I would not be disappointed with those numbers. Given you lose about 20% through the drive train, you probably have around 400-415 hp at the flywheel. Any more hp and torque in a light car like yours won't gain you much other than bragging rights because you won't be able to plant it and you'll simply wind up with more wheel spin. IMO, your headers and exhaust are sized appropriately for your engine. You can also lose some performance by going to large on your headers and exhaust. It sounds like you have it dialed in rather nicely.