Yeah player speed is something that has been continuously tuned since the beginning of playtesting. Still something I'm tweaking -- even have plans to redo how gravity movement works (right now, close quarter ground combat doesn't feel as tight as I'd like).
Right now, max speed is mostly limited by the terminal velocity of the gravity areas -- generally, you gain the most speed by falling at terminal velocity and using the grapple to swing yourself under a bridge or something, converting that downward velocity forward. There are a few tricks you can do to get a bit faster (jumping as you exit a gravity area will add your vertical jump speed to your forward velocity, for example), but it's not really practical to repeat this process quickly to get to absurd speeds.
Impulse from some explosives can also increase your speed, but I plan on implementing diminishing returns on that so that there's less value in spamming them.
Once you're at high speed, you'll lose speed if you turn too sharply (this is where being skilled with grapple can help) -- so generally, your trajectory is somewhat predictable and you aren't buzzing around like an insect or something crazy like that.
There's no sprint -- generally, once you gain speed you keep it unless you mess up. There is a boost, though -- this is mostly for changing directions quickly or getting back up to a decent speed, but it puts some of your health at risk so you want to be careful using it in battle.
Getting from point A to B should be fun (I think it generally is already fun, but there's always room for improvement) -- that's one of the key goals of the game