Offensive lineman have other physical traits of value though. Namely they're very large (and strong). You'd have to argue that size and intelligence are highly correlated, which seems a stretch.
My guess is that the correlation between size and intelligence is close to zero. So that would imply there's a negative correlation between speed and intelligence. That would be easy to test: just compare the results of the players' IQ tests with their 40 yard dash speeds.
And 'speed and intelligence' is not quite the correlation you want -- IQ correlates with mental reaction time, so smarties may be 'faster' for short distances because they get a head start.
http://en.wikipedia.org/wiki/Height_and_intelligence
(The talk page for this article is delightful, by the way)
Regarding size, speed and intelligence, even though they are huge, most NFL linemen will have a faster 40 than most math graduate students.
I agree that at 40 they will be faster. But for short bursts of speed, or for a run that requires frequent changes of direction (e.g. because you're being chased around) the higher IQ people will have a 'speed' advantage due to mental rather than physical agility.
I've read that modern tests show that some groups have a faster physical reaction speed, but a slower mental reaction speed -- e.g. the signal gets from eye to brain to hand slowly, but the hand moves fast.
note: I played tight end throughout high school. I'm a bit distraught that this infographic suggests that the offensive tackles might have been smarter than me.
The thing is, some people will start to grab it fast (high mental reaction time) and other people will actually touch it sooner (slow mental reaction time, faster physical reaction time). If you're running in a zig-zag pattern, this would mean that you would start turning faster, though other people might be able to execute a complete turn (start to finish) faster despite lower IQ.