Thanks for your reply. I knew the speedometer would be off so that wasn't a big concern but, I guess, my REAL question is would I have better traction with the smaller snow tires vs the larger all-weather stock tires? My biggest concern is winter driving and I thought since I already had the snow tires, would it be worthwhile to get a set of rims to put them on.
Not sure what model and tire size you 25 Nox has. If they are also 225, then the width would be the same and the traction should be the same. Circumference (17, 18, 19") would not affect traction IMO. Profile (55/65, etc) also would not affect traction, unless you consider the height difference might affect clearance in deep snow.
The old school theory is that a narrower tire will cut thru deep snow/ slush better than a wider tire. A wider tire may have better traction on ice due to more surface area on the road.
My 22 RS has 19" OEM wheels, but I run 17" snow tires, as they cost a LOT less. But the circumference is the same so no speedo changes. The 17 are not as wide, but for me in the great white north, I prefer that for the times we do get a lot of snow. I run Michelin X-Ice and have no issues in ice or any condition.
HTH somehow