I've had Avon M550s (all season) for about 15 months and 15K miles. At first, the tires were quiet and then at 6K miles, the tires started getting a little noisy. As the miles piled on, the tires got noiser and noiser. At 15K miles, they're deafening and they still have about 40% tread left. It's too bad because the tires have great traction and braking abilities and they look good too. The tires are also prone to to inner edge feathering. The only way to get around this is to rotate every 2.5 to 3K miles. The tire noise is just too much though and reviews on the Tirerack report the same thing.

I've learned these things when it comes to the G/Z chassis:

1) Do not run directional tires
2) Do not run tires with non-connected inner tread blocks.
3) Rotate every 3K miles

 

I was thinking of going to those tires next. Currently I'm running the Avon M500s but with the distances I'm driving these days, they wear out way too fast. I was hoping that the M550s would be a better alternative. It's really frustrating finding tires to fit the stock sedan wheels. What tire are you thinking of going to next?

 

I currently have the Avons on my rears of my Coupe with 10,000 miles. They are pretty much shot with maybe another 1,000 miles left. The middle treads are worn down. I had them on the fronts but the noise after 6,000 miles was deafening from the feathering and I had to take them off and got the original RSAs from the dealer for free. One thing I can tell any G35 owner especially for the Coupes. DO NOT GET AVONS!!!!!! They are horrible for noise and feather badly. Never again for me.

 

Terrible noise with the Avons. Wear has not been a major problem, and they seem to handle and ride well. But they drone like crazy!
It's unfortunate more folks had not reported on these when they first came out.
I would have stayed away.
Pick a tire that's been around a long time, and most people seem to like.