For comparison.
USC's Mike Williams ran a 4.59 and 4.61 according to espn's Len Pasquarelli.
Mike measured in at 6'4 229 at the combine, but when he first came to USC he was 6'3-6'4 and 200lbs the same size Spain is now.
I'm not comparing the two talent wise, I'm just pointing out that both are similar in size at the beginning of their college careers and Mike did pretty good despite his blazing speed.
Also it was said by both Damon Benning and (I believe Sean Callahan) that Spain was the best WR in 7 on 7's this summer. Fwiw.
So if Spain is 6'3 and 200lbs and runs a 4.4 or 4.5 and was also the best WR's in 7 on 7's this summer, I'm sure he'll be ok in this offense...