high speed charging is a separate issue to charge voltage.

I don’t have data at hand, but it is generally easier on lithium ion batteries to charge (and discharge) slower. I believe compared to charge voltage, that is a relatively small effect assuming the product is designed for it and manages things like heat. In a product where heat is poorly managed and builds up during slow charging, all bets are off I suppose

charge voltage on the other hand has a well studied effect on battery longevity. reducing the max charge voltage (or increasing the minimum discharge voltage), can extend the number of cycles the battery will last without degrading in a huge way, more than doubling cycle count (depending on where those limits are set, ofc.