To me it's always about the bones first. Very different ride characteristics between those two frames. Do you want a heavier skinny-tube steel frame with a more forgiving ride, or a lighter fat-tube aluminum frame with a less forgiving ride?
I think that's a more significant difference than anything that might be going on with the parts and such.
I jumped on the C'dale wagon early on, had matching twin R400/ST400 frames. Granted this was back in the day before we had nice light, supple clinchers, but the C'dales were a very different ride than the steel frames I'd been riding.
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Fuggedaboutit!