best looking into ways of improving traction to get the power down. what's the condition of your tires ?
no real point revving a turbo car past 5500 rpm as the boost pressure will drop off the little Ko3 turbo.
maybe consider some weight reduction. depending on the mileage u do dump the spare wheel and tool kit in the shed and chuck a can of tire foam in the car just incase.
check the general condition of the engine, my boost drops off very quick , so i'm guessing I have a boost leak some where.
then its the usual flow upgrades, get more cold air in, get the hot exhaust gases out quicker