I have no doubt Countach's and early Diablos were basically some parts shaken in a large metal drum - and they were bolted down where they landed.
This means clutches, syncro's etc can get abused and broken easily.
But I seem to recall that a well maintained (ie you throw money at it annually) Diablo can be reliably run to 200mph regularly - but don't do to many standing starts you will fry a clutch a week
I will look it up later - but of the top of my head the C5 Z06 runs 0-150 in 23 or 24 seconds.
The C5 Coupe runs 180ish-mph in 5th gear - the C5 Z06 runs 173-4-5mph (depending on whose calculation you use) in 5th gear.
The C5 6-speed cars are gear limited on top. Well - not technically - see the ECU has both a throttle limiter and an injector limiter - you can only run to 174ish in 5th @ 6600rpm.
The throttle control cut-off is 9000rpm in 1-2-3-4 & 6 - but 6600 in 5th, and the fuel cutoff is 6600 in 1-2-3-4 & 6 - but 9000 in 5th.
There is also a speed limiter in every gear, and I think it is set to 254mph by default.
What they have done is made it a little less abrupt when you run into the rev limiter at 174mph. They close the throttle on you - not the fuel... but in every other gear they leave the throttle wide open, but cut the injectors off. This is why when you run into the red in 1st or 2nd or 3rd or even 4th its real abrupt and very noticable.
But in 5th it's almost like the car can't push through the wall of air - but this we know is not true, because the higher geard C5 Coupe pushes on to 180mph with only 350hp. Folks who have set their ETC (electronic throttle control) to 7000 in 5th have run right up to the limit and on to 180+.
It is how ever advisable to not do that with the stock valve train