I think it needs to undercut the Polo GTI, or at least match it in price, given the Polo is an auto (yes, I know it's not a "real" gearbox for some of you, but they are usually about $2k more).
Anyway, here's some footage of someone driving a Fiesta ST on the Nurburgring.
http://www.youtube.com/watch?v=D4EGZlNmvU4