The AUII XR8 has no knock sensors (unlike the state of the art LS1 - you have to admire chev with things like composite inlet manifold etc).
Ford state minimum 95 RON - this is equivalent to above 98 octane rating. In NZ we have only 96 octane (about 93 RON). You can get 98 if you are prepare to hunt for it. What long term damage will be who knows, but you can bet your last dollar that problems will display themselves after 100,000 km, therefore will be not a 'Ford' problem. Would be interesting what a Ford dealer over there advises on octane rating to use.