The picture with the red wheels above is using 16 inch rims...hence the sidewall flex.
I am currently running 15 inch stainless/chrome rims as shown in the picture at top.
I have played with the tyre pressures quite a bit. Most recent experiment was to adjust from my usual 24psi for front and rear (cold) to 27psi front and 22 psi rear in order to try to offset my fairly strong oversteer. It seemed to wrok rather well I must say. Front tyres started to scrub a bit more so the back end was not as twitchy. Running 24 x 24psi was making my back end quite squirrely. As you can see if you google "Aceca" and "Fisher" together and then click on images, you will find many pictures of me with a wide end slide. Looks good in pics, but I can assure you, it's not the fast way round!
The key thing for me is to be able to justify using Michelin radials to the authorities if it is indeed "period correct" AND better for the car in terms of handling. I did drive on radials last year due to a shortage in Dunlop supply. The handling was much tighter, although at the edges, the radials had a nasty habit of snapping loose without warning. Took some getting used to in comparison to the usually gentle and predictable non-radials.