Ringed chains on a 125 is insane. Unless you are slowing the hit. The alloy or steel rear sprocket? What good is a rear sprocket that lasts longer than what? The steel rear sprocket loses less than the ringed chains on throttle response, imo. BUT, 1 part goes bad,ie, the front sprocket, you replace the rear sprocket and chain, the chain goes and so do the sprockets. So why buy a chain for double the price, and that outlives radiation? The sprockets will not last that long! There are limits on cheap chains and sprockets, they are like butter. What ever you get, its a dirt bike. Dirt, sand, horsepower and neglect will destroy what ever you buy. A lot of riders idea of a good chain and sprockets will vary! Don't make me get the "book". Vintage Bob