Having owned both I can happily say that I'd expect a Sports Fiesta will happily provide a driver a much better handling ride than the likes of the ST170.
I had 2 Zetec Fiestas from new (1 diesel, 1 petrol) and an ST170 from new and the Fiesta offers a better driving position and an awesome chassis. Indeed the engineers who worked on the ST have said that it is quicker on certain tracks than the Focus RS. Says it all to me and remember the Fiesta chassis is much newer.

Please bear in mind though, it is like comparing Moet & Chandon to a rather fine Bollinger.
