You say ALL OPC's are highly tuned ? I have a few friends with Astra OPC's and just a chip gave them serious gains ( just like the GTi). Like you, im not an opel fan so i dont know much about the Corsa OPC, but the Astra OPC apparantly has a K04 turbo, but thats besides the point. My point is, a chip will make the Corsa OPC much faster and quicker.
The Corsa OPC is a very nice package, but at R230k I'd rather buy something else. I read somewhere that some poor soul didn't want his Astra OPC anymore and got a trade-in value of R170k
Anyway, I personally wouldn't chip a 1.6T, especially one from SLOPEL