I agree mine is always best on Tesco 99 too. Maybe for Lawson77 it is something to do with where you buy your fuel i.e. if bought from a Tesco that barely shifts any super then it may have been sat there a while. [/quote]
I did a TD at Oulton last year and filled up at the Shell. Car felt like a bag of sh*t until I had run the fuel through the system - was 99 Optimax but guess it had been sitting there for a while
S1’s don’t have a knock sensor so unless the car is mapped to take advantage of high octane fuel it won’t make any difference power wise. S2’s are equipped with said sensor so are able to run more advance with high oct fuel and as such make more power. But I guess it all comes down to the ECU parameters 
2008 Exige S with Gotham tune needs 97 oct. min or she can pink
S1 VHPD will not run properly on 95 octane (ie pink like hell), despite what it says in the Handbook!
That’s interesting, as you say “regardless of the handbook” the VHPD must have been mapped on high oct fuel, or it was just badly mapped, I would hope it was the former though