I've worn out my "stock" chainrings on my Shimano M770 crankset and am need of replacements (all three). I'm wondering if anyone has a recommendation insofar as purchasing new chainrings: i.e. should I just replace them with new Shimano M770 rings or should I put something else on the crank? I've heard that some other aftermarket brands sell chainrings that may not be the lightest in the world but will last me longer than the factory shimanos. Any experience here? BTW - I run Shimano "shadow" deraileurs and a 10 speed "ultimate touring" cassette from Sheldon Brown.