As someone who has owned all of the these - may I comment?
Forget the Gsi - too much dead weight & too costly to modify & finding one that hasn't rusted away & hasn't got starship mileage is nigh-on impossible.
The 200 SX would be good & is very much in favour with the drifting crowd.
The MX5 makes a great trackday car for the following reasons.
It is relatively cheap.
It is light in weight.
It is rear-wheel drive with excellent steering, brakes & gearshift as standard.
It has fully adjustable suspension as standard (caster, camber, toe-in ) on all 4 wheels & believe me this does make one hell of a difference.
There are lots & lots of tuning goodies available for the 5, with the right supercharger or turbocharger you can easily take these to over 200 bhp for £1500 or so - 300 bhp is in reach if you want to spend a say £5000. Enough for a car that weighs a ton?
There is the Spec Miata racing series in the US which is a goldmine of information re different suspension settings, wheels tyres etc.
And lastly its different - people do get
very wound up by being beaten by a "hairdresser's car" - which makes it even more fun.
Have a look for more info on this forum
http://www.mx5ocforum.co.uk/viewforum.php?f=16