Perhaps this link might assist you in comparing the SMSP and Hytech. If you look at the dyno curves, they are essentially the same. I would imagine no real live person could tell the difference between these two based on the "butt dyno". I am not sure about the editorial comments in the link, but you can make your own judgement by looking at the dyno curves.

http://www.importreview.com/reviews/smspVShytech.html

Gain seems to be about 18 whp (from about 162 stock to 180 with header). This almost matches what Hytech says. Their website says you get 22 whp gain. This could be due to different exhaust systems used after the header. The link above does not state what exhaust was used.