Im with OC on this.. I/H/E are the biggest waste of money when you have a motor on stock internals.. I know.. Ive Been there, Ive done that.. It was the most money Ive ever spent on visuals for my car.
Just like OC said, even though you may gain a hp or 2 at peak, you have just lossed hp at other RPMs.. To me its more important to have a nice flat torque curve then a short peak anyday. It increases the driveability of the car overall.