While speed I think speed is a very important part of the position I don't think it is critical. If he runs a 4.5 without pads then fine if he runs a 4.5 on with pads that is another thing.
There are lots of speed guys out there but when they put the pads on it changes. If they guy has decent speed with pads it is all the better. Coker lacked a lot of top end speed but was still successful. How the player moves laterally, hits the hole with quickness and has vision is more important (something I think Coker struggled with last year at times). Prime example is Emitt Smith, not great speed but had good vision and was able to hit the hole. Helped when you had an awesome line too
Another quesions is how are his hands? I think Iowa needs to develop more pass plays to the RBs to deviate from some of their formation tendencies.