Help me spend money on wheels

[CWilson]

I am doing the PCGB track day at Silverstone next week and on looking over my car carefully have found my tyres are not even legal for the road let alone the track (cracks in sidewall). In looking around I found several options. For the very little more than the price of new tyres I can get a set of 17 wheels with new or barely used tyres. I called around and have narrowed it down to :

A used set of Michelin Pilot Sport tyres (tread 6.5mm Front, 4.5 Back) £120+VAT and Shipping
New Pirelli P6000 205/55/zr16 225/50zr16 £350 Installed
996 C4 Wheels 205/50/zr17 and 255/45/zr17 (used tyres with 12000 miles) £475
(Worried about more understeer)
New Cup 2 7.5/9 with new Yokohama AVS Sport Tyres £650 - £150 Trade in

I am also replaceing brake and transmission fluid. Does anyone have recommendations (remember its a Tip)