Hyperkid - YES!
Pieoter, have a look here :
http://www.drive.com.au/buy/new/car_...15916620050609 ; the Lotus Elise would be one of the best handling cars this side of $100000. Check out the tyre sizes used - front 175/55R16 and rear 225/45R17. Now that gives sidewall heights of 96.25mm for the front and 101.25mm for the rear. The rear rim width is 7.5".
Now compare the Fiesta Zetec sidewall height 195/45 = 87.75mm (WOW! it's LESS!!); now I think the Fiesta might be lacking in other areas than tyre sidewall height when it comes to handling..... Money would be better spent on things like shock absorbers, decent springs and swaybar upgrades (or even just bushes), that rear hub spacer kit from the UK etc. There is lot more to it than simply increasing the rim diameter.
Even a car like the HSV GTO with 245/35R19 tyres has a sidewall height of 85.75mm - only 2mm less than the standard Fiesta Zetec 16" tyres. The MY06 Subaru Imprezza STi runs 225/45R17 - sidewall height is 101.25mm
So, is the sidewall height on the Fiesta with 16" rims really the issue that is affecting the handling? I think not- money would be better spent elsewhere. ;)