I think there a difference between speed and quickness. Speed is how fast you can run at top speed, quickness is how fast you can get to top speed. I saw stronger DL/OL players beat this year because the opposing line was quicker off the snap of the ball. A line player does not necessarily have to be fast but I think they need to be quick and then the strength factor kicks in. You could be strong as ox but if you are constantly beat at the snap of the ball you are going to be out of position .Of course that also depends on the top of offense you run, if you pull guards and tackles a lot you are going to want them to be fast.
Your better backs tend to get to full speed in 2 steps or less, where as your power backs tend to be stronger and harder to bring down. I would say quickness, speed and then strength. Technique (as well as execution) can overcome strength and some speed but in the end usually the fastest teams tend to win, hence why the mountain teams have such a hard time with teams from the north.