It depends on how you use it. I've seen a lot of combats where that extra movement isn't being used, and it's just another hit on an enemy to try and burst them down. But that's anecdotal- it has more potential use, and you may have seen that.
Just as in games with more or less combat, a 20 Strength vs. an 18 Strength is potentially a big deal or barely worth mentioning. All anyone can do is point towards trends, but even if we were to run a whole campaign, from 1st to 20th level, with two characters who are clones of each other, save one has 18 Strength and the other 20, and come up with actual numbers of how that mattered over the course of the game, no matter how great or small the effort, that's still not what happens in your game.
No one can predict the future. Maybe Starsky is played by that one guy who should go to Vegas every weekend, and Hutch can't roll above a 7 to save his life.
All anyone can say is "in general, this is probably better from a pure math standpoint". The player has to make the individual choice, and live with the consequences.