Actually the Pandas 13" tyres are perfect. With a 54bhp engine the last thing you want is to have modern fat wide tyres. The profile of the tyres also helps the ride quality from what is quite a basic chasis.
The Panda is a budget car and as a result does away with the silly low profile tyre crap. My dads Fiesta has low profile tyres (standard from Ford) but has a 1.3 push rod engine, all the tyres do is make the ride quality worse.
I just cannot imagine anything than a Panda riding on 205/40/17s.
The Panda rides like a boat because it is a budget car, it is essentialy the cheapest new car you can buy at the moment. It costs the same as a three year old Fiesta. For most pot holed city driving though I still much prefer the comfort of the standard setup, it is just a damn shame about the lack of a rarer ARB.