I'm interested to hear the verdict on which chain to go with. I'm considering going for a KMC next chain.

As per the cassette, I'd say go for it if you want it. I ride a 12-25 6700 cassette (6700 equipped bike). I'm looking at picking up a new cassette for a possible new pair of hand built wheels, and will most likely go either 11-25, or 12-28 (I don't really need the 28 unless I go mid-compact chainrings - which I've also considered). Saving weight is your call. With 6700 cassettes coming in around $50 or less if you shop around, that's a solid 1 g/$ saved. To some people that means a lot, to others it means nothing. Personally, I'm on a quest to go sub-16 pounds with my bike, so 40g saved on the cassette (especially with the quality of that cassette) would be solid compared with g/$.

Just saying. Before more of the "get a haircut" or "go use the bathroom before you ride" posts get made.