I would recommend just some bottom end work. Look into some forged pistons and connecting rods so you can turn the boost up.

You may want to also look into some bolt-ons to make the setup a little more efficient. A wider downpipe, high flow cat, 3" exhaust, itr/ctr cams, larger injectors, and some better form of engine management (assuming you don't already). Some information about the setup would be nice in helping you out.