I had a look on
www.tirerack.com and couldn't see the latest Continental Sport Contact 5P tyres listed under 275/35/20.
I think you'll find if you check you've got the wrong information for a much earlier version of the Sport Contact tyre.
Last Sport Contact 5's I saw here in N.Z. were just under $900 and that was for a 245/35/19 size tyre...it was THE most expensive tyre I could possibly buy for my car with its stock rims. I think if you re-check you'll find HSV have spared no expense whatsoever on the tyres, in fact quite the opposite to the extent that they make quite a meal out of their tyre selection in their marketing material.
Like I said earlier, the stickiest, softest, best gripping tyre they could possibly fit.