I totally hear you on the durability thing, but I think the lack of availability of steel sprockets is because they're just isn't a need for them. I've never heard of anyone have a rear sprocket wear out before a chain, so I'd go stick with aluminum for the rear sprocket for availability reasons... If you want extra life get a hard ano sprocket.
You're right, less weight in the drivetrain is the motivating factor. Also, a modern 525 chain is ridiculous overkill for a 600cc bike. The tensile strength on modern chains is very, very high, and even literbikes can run 520 chains these days, so there's no reason not to go 520.
BBD - my front sprocket went on with no problems. Or there are problems, and I haven't noticed them!
And you 4X10 bastidges are very lucky. My work week usually looks more like 5X10 with a few hours on a weekend thrown in for good measure! I haven't spent nearly enough quality time with my bike this year

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