Thought I'd read somewhere that X ring chains sap a fraction less power??, less friction hence less heat, less likely to chuck the lube off??
I've been thinking that chains stretching are a bit of a chicken and egg job, frequenty "tensioning" 'em leads to a need to 'er tension 'em more often
Me 998 chain lasted well over 12K miles and in reality it only had to go when the front sprocket showed signs of wear so it was a new chain and sprockets job, maybe the front sprocket was wearing cos I run the chain slacker than some might, I dunno.
Ray.