I had one at 284bhp with minor mods.

It depends on your budget or as I did bit by bit.

Doesn't really matter to much to start with.

I went panel filter and remap.
Cat back with decat
RS clutch (weak point on 2006 models)
RS plug (cheaper than ST)

And got 284 with just that.

Ideally I would of then got turbo down pipe (get new bolts as the originals snap easily)
And intercooler as they are shite! And induction kit.

From there RS injectors and bigger turbo with map to suit.

Someone with better know how may (and please do) correct me if I'm wrong.

Have a look on the STOC as ell. Loads of info on there.