Updated the OP with Carlos’ info and a list about brake rotors. feel free to add more guys, I’ll add it in.
I haven’t been in the lightweight game long enough to really give tested/honest feedback, but it certainly will make a difference when you put the right parts in the right place. The most important thing, in my opinion, is to make sure you’re spending the money wisely on parts to shave weight, not just spending the money to shave any amount of weight that you can.
I.e. spending $100 to go to a lw battery when yours is on it’s way out and dropping ~35-40lbs of dead weight, GREAT idea. But spending another $400+ to shave ~45lbs on a battery, horrible idea imo. Realizing diminishing returns is the key factor to keep your sanity.
In that same regard, the cf hood argument some raise is a great way to save weight, but for $1500, there’s a whole lot of other ways to shave weight and increase performance that will far outweigh (pun?) the gains for the cf hood. Rotational mass is huge, and not to add more misinformation, but an old reference is 1lb of rotating (unsprung) weight saved is equal to ~7lbs of sprung/dead weight. No, this is by no means a perfect/exact translation, but that gives a perspective how saving weight on wheels, brakes, flywheel can all make a REAL difference.
I know when I switch over to my lw wheels, its just shocking how fast the car gets up and rips through first gear. It almost always takes me by surprise and is a further testament to the gains they provide. It’s tough to feel them when at speed (just like hp is tough to feel vs how impressive tq feels), but at slower speeds, the difference is noticeable.