Lol That is my only addition. Just because it is my favorite car EVAR.
I do not know if it has been said before, but fast is a human turn used to describe a sense of speed or quickness and since it is a human term it is subjective to the topic and person applying it.
Fast has no comparable unit like speed (mph/kph), power (bhp,lb-ft), grip (g-forces). All of those things have a role in the application of fast, but your fast is different than my fast.
Example: A lot of you guys are using 1/4 mile times as a defining measure of "fastness".
However, I think it should be road course times, skip pad numbers, or a combination of the two.
I like cars that will not only hold me to my seat, but try to sling me out the window and bash my face into the steering wheel. I like a car that accelerates quickly, but grips and brakes like there is no tomorrow.
I think power to weight ratio is a decent indicator of being fast if we want to gauge just the speed aspect, but it does not take a lot of things into account.
I think that the "fastness" of a car is too fast and subjective to actually put a label on.
Then again this is all my personal opinion that I just typed up as it came to me.