There are lots more variables that just the string material. How the string is made, how many strands (overall weight including serving, silencers, etc.), tuning, your release, nock fit, if the arrow is properly tuned for the set-up, brace height, etc. etc. etc.
Apples to apples (everything equally tuned, nocks fit correctly, brace set correctly for each one, arrow spine correct for each one, etc.--not just swap strings, set the brace the same, shoot the same arrow, etc.), a high performance material is going to have little to no elasticity. That's the big difference. On the shot, it will have less vibration. Long-term it won't stretch/creep anywhere near as much, will last longer, will be more consistent.
I personally am not a fan of "skinny" strings, or fat strings either. I've never owned or even shot a bow (that was built for them) a bow that didn't benefit in some way from a high performance string. I don't know about speed...can't remember the last time I shot a bow through a chrony, or even where my chrony is.
As an extreme example imagine trying to release a fishing line off your fingers vs a handle on a metal bucket if both had a 50 pound weight attached to them and you were holding them by your side.
Never understood why some folks say one material is harsher on their fingers than the other, at least when served correctly. With the right serving, both with have the same size "handle". Feels the same on my fingers.