Chip is the best option and best bang for the bucks.
In the US the best software seems to be GIAC and APR but should not cost more than $500 max.
In the UK ther are a lot more options and REVO, JABBA Sport, GIAC (quite new here) Superchip and loads more other indepents that do great prices on chips from £250 upwards.
As stated you should see power increase around 30-40bhp but I would also change the DV to a upgraded unit and if you want a little more power add a exhaust to help free a little more.
Other than that you will looking at changing the turbo.
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