Just keep sprinting but have longer rests (since your looking for speed not recovery).
The fact that you are powering out of the start and then dying means you don't have the stamina for the distance but have the strength (indictated by the lifts).
I am not a sprinter so I can't really comment about the upper body thing, but that doesn't sound right. It just seems that even though he isn't as strong, he has more stamina (from the lower weight I would gather) so when your dying he just sails by because he lasts longer. He may just be focusing on the arms and not realise that they have sweet F.A to do with it (but thats my opinnion).
I think cocksprinter would be your best bet really, he is a sprinter after all.
How longs it taking btw, 100m is like 12-15s (depending on fitness).