I would like some numbers too, but it's a known fact that the WRX runs very rich (just look at the black soot on your muffler) so the tune "leans" out the mix a bit. A leaner air/fuel ratio means a bit more power (if done safely) and less fuel used.

The general acceptance is that the stock trans on the WRX is its weak point. Most people think 300-350hp is its limit.

The signal to noise ratio at www.nasioc.com isn't as good as it is here (understatement) but I've gathered most of my information from there and from calling Cobb directly.

I've had mine for about a year at "Stage 2.5/320hp" with no issues. Knowing that nobody can start my car even if they hotwire it was worth the price for me.