Need Snow Wheel/Tire Advice

[jlkohio]

I'm about to buy snow tires and wheels for my 2005 X5 4.4 - Sport+Premium that currently has the 19x9 - 19x10 offset setup with Michelin Diamaris all around. Most say that the recommended winter setup is 18x8.5 with 255-55-18s all around. I was wondering how much snow performance I would lose if I got a set of 19x9 (all around - no offset) with 255-50-19 Pirelli Scorpion Ice and Snows.... If I lived in MN or MI, I wouldn't even bother to ask, but here in central Ohio we haven't seen more than 4 inches of snow fall at one time in many, many years. I wonder how much difference is in .5 in of width and 1 inch of wheel height (or 1 inch less tire sidewall)...

Experiences / opinions?

Also, feel free to share your opinions about your Michelin Diamaris. My first set lasted 11k miles before they started cupping. It made my drive sound like I was riding on a train. The dealer talked me into a second set....at $1850 installed with alignment... and now the new set is beginning to do the same at 10k miles. The harmonics are totally irritating at 80 mph as the road noise makes a oscillating "wah...wah...wah..." sound.