I always struggle with this question. Largely because I can't understand why so many people spend fortunes turning perfectly good road cars in to a bad compromise between road and track. Not wishing to upset anyone, just my honest opinion. [&:]
Having been driven round a track in a few very well developed track cars, Peter Empson's white car and a certain little Honda spring to mind, makes me realise just how good a dedicated track car is. Pretty much every car that's trying to be half track/half road car seems to cost it's owner far too much and then be good at neither.
My question would be what do you want out of a car, and what are you not getting from the 944 at the moment? If it's just a power thing, get a cheap 'Vette and have a laugh in a straight line. If it's a track toy then get something you can trailer there and not be compromised. Different cheap cars for different uses.
Personally I can't see how your particular 944 would be improved for regular road use by spending money on making it faster. It seemed to be keeping up with my S2 on the way to Frontrunners without any noticeable issues, and I can't see how we'd have been going any faster or having any more fun on the public roads without being stupid. Surely upping the power will only make you reach the responsible limits a tiny bit quicker, and be more frustrating?
So. We're agreed it's another car then. [

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More details please. Are you after a real classic, like an MG? A modern classic like a Quattro? Something mad like an old Aston? Possibly a V8 Aston, I like Astons. A Virage, perhaps? Proper old Vantage? [&:]