Well clutch will always give up if you keep it stock. if you go turbo you might want to change the clutch too. I am surprised that they even raced with stock clutches, they were not geting the right power to the ground. B/w the engine and the tyres the clutch plays a very important part. if you do not have the right one, you do not have the right power.
As for your VTi it would last you sometime before you end up changing it that is if you keep the boost b/w 6-7psi that should give you some relaibility. But remember boost is placing extra stress on your cars internal and drive trains and they will give in at some point.