You're saying the 40 yard dash is the most important thing? Well then why stop at 40 yards? Let's time these guys at 100 yards ... or even better 1,000 yards ... or how about 10,000 yards, that'd be even better right?
To me, there are 4 aspects that are very important measurements of 'speed' that really matter for an OLB/DE: first step quickness, acceleration around the edge, ability to maintain speed while being blocked, and lateral agility.
The first step quickness is usually shown in what is sometimes called the "10 yard split" of the 40 yard dash. After all, most OLB's run anywhere from 7 to 15 yards to reach the QB, rarely more than that. So, top speed isn't usually the determiner of whether they can beat their blocker with speed. Long doesn't have a great 40 time, but his 10 yard split is pretty good, because he actually has a good first step. No, he's no Groves or even Gholston, but his first step is good.
Acceleration around the edge is something at which Jason Taylor is absolutely astounding. JT has a quick first step, but it's his acceleration that allows him to blow by his blockers. Coupled with his long arms many LT's think they have good position and he blows by them effortlessly because of his superior acceleration. Long's acceleration is good but not great, Gholston definitely has the advantage there.
The ability to maintain speed while being blocked, which I'll call blocked speed for short, is a combo of what we consider 'speed' and 'strength.' Many very fast pass rushers fail because they're sprinters more than football players, so when the LT gets his hands on them they simply lose speed, leverage, angle, and are completely taken out of the play. While Gholston is clearly the stronger player and the faster player, Long has significantly better blocked speed as he can maintain his rush very well while being pushed behind the QB. Both are good bull rushers, but that's not what I'm talking about, I'm talking about using their speed to get around the outside of the LT without being slowed down to innefectiveness, or being pushed past the play as the QB steps up.
Lateral agility is the ability to change directions. This is crucial for spin moves and double-moves, and often is dependant upon having good blocked speed as well to pull these moves off. Long and Gholston both accel at this, but Long is better.
The stages of a pass rush are more than straight speed and almost never cover 40 yards of field. Safety blitzes or corner blitzes sometimes do, but not OLB/DE pass rushing. Those types are generallly unblocked sprint races timed against the QB's ability to get rid of the ball. Usually, OLB's and DE's are accounted for in the pass coverage with an LT, sometimes a LG or RB will help, but it's neither a sprint to the QB nor is it going to cover 40 yards. So, when you're looking at an edge rusher, you need to veer away from the generic 40 yard times and concentrate on the metrics that really matter. If you're interested in pure speed, then perhaps the 10 yard dash (called the "10 yard split" when they list the 40 times at the combine) is probably your closest metric. Unfortunately, it's done in tights from a sprinter's stance, instead of wearing pads and a helmet from a typical OLB 2 point stance. Still, the faster players at the combine tend to be the faster players in pads as well, although everyone is slower on the field than they test on the track, and not everyone slows down exactly the same amount.
I love the combine, and I really like the computerized times because good, bad, right, wrong, it's even for everyone, so while you can't always compare this year's time to last year's time, you can compare all the players at this year's combine against one another.
To the OP, I'm curious where Long's 10 yard split appears compared to other top 6 LB picks of the past. I realize he's 272 pounds, so he's not going to be competitive with the 220 pound LB's of the past, but I think his time might be a bit better. I'm interested in your results.