Put it this way i have spent nearly 2grand on my ST170's engine and all i have to show for it is 189bhp, there is not allot of tuning potential here as a N/A engine, even with TB's you will only see 220ish, the weak point is the oil pump, they do not like to be revved past 8000rpm so unless you plan to switch to a dry sump set up i would go for forced induction or buy a faster car. Lairy cams generally mean higher revs, even billet oil pump ring gears have been known to fail at high revs. The standard black oak managment is not an easy unit to tune, the best thing you can do is get a generic map unloaded from the likes of Dreamscience.
You can only fit a verier cam to the exhaust pulley due to the VVT on the inlet side, i have a CFM one fitted to mine retarded 6degrees, it gained roughly 5bhp for this mod, torque of the devil will supply fit and set up the pulley for £350