550 alternative wheels

Hi,
My 550 has the standard wheels, which I like the look of but I'm frustrated by the lack of tyres available. I run the car on the standard Pirellis but do most of my miles on tracks and the more track focussed tyres, such as Corsa, don't come in that size. I seem to have three choices (i) change the wheels, say to the 575 size (ii) put a lower profile tyre on my existing rims (I can get 18 X 295 x 30 Corsas for the rear but that will change the rolling radius) or use a different make of tyres, but I'm not aware of a better alternative than the standard Pirellis.
Advice from anyone who has tried any of the above will be very welcome
Thanks
BlueMaranello

 

Michelin PS2 great tire