Thats pretty good for just a chip and an exhaust.

If you have a look at the RSownersclub website you will see quite a few cars that are running over 300bhp.

IMO you will require
Chip (which you have)
Tubular Manifold
Exhaust (which you have)
Air Intake (Gen II or similar)
Forge Actuator set to 21 to 22 psi
Roose boost hoses

I would also suggest you fit the following

Upgraded charge cooler
Change the original dump valve to a forge 007 dump valve