I know it's too late as you've already bought your tires, but I ran 235/60/17 on my 400h for two winters with no problems.
If you check here using this handy tire size calculator
you'll see the diameter on factory 18" is 28.2" and diameter on 235/60/17 is 28.1
Compare this with 225/65/17 where the diameter is 28.5".
The goal when + or - sizing a tire is to keep the diameter as close as possible to the original tire.
So you can't go wrong with either size, but 235/60/17 will be closer to the diameter of the factory 235/55/18.
I know everyone says thinner is better for winter, but does anyone out there really think 10 MILLIMETRES
(the difference between P235 and P225) is going to make a difference? Now, if you're comparing P155 width to P235 width...yes...that's going to make a difference.