Cats chaincase is a weak link, hoping this system is better. I have not heard of issues yet with the 600 but not many out there and surely not many miles. 858 is actually lighter than the 600. Also, since moving back south only put about 1500kms on the sled, the 4 stroke was a much better choice when running 5 to 6 k per season. Yet to see the price, and this season being a bust, the economy on a downward trend, leftover pricing may return so that is also a factor that may have undue influence on my decision. God, now you got me thinking........