[Sumea]

The 5cm difference won't necessarily make the wheel or tyre more susceptable to damage. They all have slightly different sidewall stiffness, and I would assume (I have little knowledge of all weather/ snow tyres) that winter tyres have stiffer sidewalls than summer performance tyres anyway.
Really. it's only when you go for a much bigger wheel and get down into the 30- 35 sidewalls that you would suffer.
I think 45;s would be fine. The 225 is just more grip.

I have 235 45 17's on mine and the ride is fine, and we have some pretty bumpy roads.

Actually the difference of 45 and 50 sidewall is 45 being 101mm (abbrox 4") and 50 being 112,5mm (approx 4,5"). Id personally go with the 45. Im running 225/40-18 on my 18x8.75" wheels.