Let's recap why most people swap to a 520. It's obviously weight savings.. You talk about x ounces weight savings.. vs. a 400lb bike.. But that's not how it works. This is rotational mass.. 1lb in weight saving is very significant. But most of the weight you save is actually on the chain anyways. So.. why are people hounding you on a steel vs. aluminum sprocket? B/c those sprockets last quite a while and pretty easy to change out. I rarely even see steel aftermarket sprockets.

Guess it depends how much money you want to dump. The typical setup is 520 conversion, w/ steel front, rear aluminum. You get the majority of your weight savings on the chain and mediocre weight saving from the rear. Sometimes very slight in the front.