nitrous is cheap and works, i'd say thats your best choice. its not a constant power adder but i almost never spool the turbo during daily driving anyways (except under bridges, going through tunnels, when theres people/cycling by the road, on ramps...actually nevermind, i love to hear the bov
)
and just to give you an idea, the hytech header/cat/exhaust combo is a little over 2g's. its about the best on the market with a 20+ hp gain (on a type r)