Not too sure about making the flag runner faster. If anything, I think the flag runner should have a decrease in speed so teams are more viable to kill, and subsequently protect the flag runner. It also makes them more vulnerable to attacks, which makes capturing the flag an actual challenge. If the flag runner is faster than the norm, he could probably outrun chasers easily. Maybe give him a +20 health boost to compensate for his reduced speed.
I'll post something more insightful after I get some rest, my brain isn't firing the way it should right now.