Thats a bit too much dude!!!
That fully depends on how well the car can adapt to different octanes. Back in Aug 06, Thorney Motorsport ( http://www.pistonheads.com/gassing/topi ... 7&f=57&h=0 )did a test with a 2003 BMW E46 M3 CSL, and as a control car a standard Toyota MR2. They saw the CSL drop 40BHP by switching from Tesco 99RON to a 95RON. Admittedly the car was mapped for this kind of fuel, but it shows how big the difference can be. Now the Zed is mapped for 98RON, so giving it 95RON over Tesco 99RON, I would hazzard a guess that you could quite easily lose 15BHP. On the fuel consumption side, I have seen many times that 99RON gets me more than enough in higher MPG to cover the extra cost (about 3 quid a fill up) over 95RON.
Also, unless you drive around for a good while with 99RON in your tank before using it on track (say drive up there on it), then you probably dont see any benefit of it until the end of the day as it takes a while for the fuel trims to compensate fully for the better octane.