GPS matters for a couple of reasons ...
Some guys just don't run as well with pads on, for whatever reason. For some guys, there's no difference (see Cooper Kupp, who might actually be faster with pads on)
Also case in point, Riley Moss is a 4.3 track guy but he's not on that list.
Some guys don't run as fast carrying a football (see Cooper Kupp again, who might be faster)
That said, I care about 2 times more than GPS or 40 ... It's the 20 yard short shuttle and the 3 cone. In my opinion, the Rams brass does as well. This is for everyone from offensive linemen to DBs. I never throw those numbers out. Not every player needs to hit a top speed every play, but every player needs to be able to move with agility and burst in short areas.
And to mention Van Jefferson here as a high GPS guy ... he may have a lot of issues with the ball in the air when it's contested ... but the issue he doesn't have? He doesn't need to slow down to track the ball in the air. He's generally running at max speed when he catches a bomb, which is why he usually pulls away late (which is not the norm)
Anyway, everything factors in. And also, Musgrave likely punched his first round ticket with that. Gonna be nearly impossible to dodge Greg Olsen comps now.