Whilst Urbanracer doesn't have the best people skills, he's largely right. You'd need a remap to take advantage of Super and the knock sensors are only there to protect if the octane level is below what the engine wants.
What I would say is that a family friend was in the supply line for petrol stations and the only thing he suggested was to avoid Jet stations and only use Supermarkets as a last resort. Jets get the cheapest dregs and Supermarkets are price-led too - although given the throughput they have, it's less of an issue than a Jet station. My pick would be to use a mainstream petrol brand, but not bother with the super version - standard Shell has detergents in it anyway.
My old track car was mapped on super and (not living in the centre of civilization) it was sometimes a proper pain in the arse to find some when you were needing it and hadn't planned...