TBH it's all a bit new for me.
I thought 950 was 9 speed anyway though? Or did that come with 960?
9 should work on 8 as yes, thinner spacing. 9 Won't work on 7 or 10, but pretty sure it does on 8.
Weight?
No idea, and no means to measure I'm afraid. Imagine the lightest thing you could get that would shift gears, and you would probably come up with these.
BB.