@Drew - thanks for all of that. i certainly want to avoid spending so much that "lightweight" overshadows "durable". i weigh about 2.2 pounds per inch (most people think that's skinny enough!), but i'm not competitive and i've usually got my pannier bags full of stuff.

any advantages of spending more than $15-25 on a steel chain? i usually just do a dry-lube from a spray can on the chain and cogs (this seems to attract less dirt and grime than oil). because i ride in all weather and there's no layer of oil on the chain, my current chain does get some "surface" rust but it never stays still long enough to be a problem (AFAICT). this makes a stainless-steel chain (9SX) seem appealing.

right now my immediate concern is: what if i put on the new chain and there's excessive wear on the gears? should i just replace with similar? or spend a bit more and "upgrade"? in a way it seems silly to just replace deore with deore (especially when the XT stuff is so sexy)... OTOH you're making it seem silly to replace deore with XT (unless i'll be entering the bike in competitions; which i'm not planning on).

if a new chain reveals excessive wear on the cassette and chainrings, then i'll probably put the old chain back on and just run it into the ground. that's when i'd have to accept the possibility of something bad happening, and me walking home, pushing the bike.