hmmm. I know someone who owned an F40 and F50 (He had to sell them together in a deal).My friend with the 275 (my avatar) has driven them back to back on a local freeway. They wanted to see what the differences where.
Basically what he said was that it was amazing how easy the F50 is to drive. Very little drama, even all the way up to 275kph or so. He said the only thing was you had to get used to the vibration and even the noise. This is because of the F1 way of bolting everything directly onto the chassis.
By contrast the F40 is a beast. He says very twitchy and nervous, but he also said both of them would choose the F40 over the F50 (They are/where both racing drivers). This is because you do not want this kind of supercar as a daily driver. You want a seriously fast car when you want it. So the relative ease of the F50 is a bit of a waste.
In their impromptu race (High altitude, so the F40 had an advantage with turbos) the F40 has the faster acceleration. The F50 only started inching closer at around 260kph, but not rapidly in any way.
About 6 months ago my friend was driven around Kyalami in an Enzo. He said the most impressive where the brakes, pointing out how they would accelerate past a 360CS while it was already braking for the corner. According to the owner the car is really easy to drive, seemingly shrugging of its weight and size. It has so much power that the acceleration truly awesome(My friend also mentioned this). But he also said you can't deny its size. Its a big car.
And lastly my friend used to own a 288GTO back in 1988 before selling it in the price boom. And he recons the GTO is what you want if you want a supercar on the road. Easy to live with and seriously fast in its own right((He saw 300kph on the clock). The F40 for something special that you can race if you want to.
All in all the F50 seems to be the one left behind.Not as spectacular as the F40 and not as technologically impressive as the Enzo.
The former F40/F50 owner is now trying to buy back his F40.
