I've missed Donald's blogging at Back of the Envelope since he slowed down his rate a lot (sort of like I did...), but he seems to be picking up a bit lately. I was almost inspired to write a long response to his post on Superspeed, but I rested a bit and the ambition went away. So just a few thoughts:
If you are assuming that superspeed and superstrength work simply through normal physical processes, then Donald is right that superspeed requires superstrength, but it also requires enormous energy and more oxygen than normal lungs can take in (assuming that you extend it for any length of time). It also requires superendurance since a person who is running really fast will go a very long way in a very short time. Additionally, superstrength requires supertoughness.
1. super energy (this could have applications on its own like holding your breath indefinitely or surviving blood loss).
2. super endurance
3. super toughness
4. super strength (requires 3)
5. super speed (requires 1,2,4)
Of course all of this could interfere with a story, so maybe it's better just to let it go...