I just bought a SRAM PC-850 for my 9 speed Lightspeed. I assume that this is incorrect, and that I would need the 950 version? Thanks.

I'm not a mech, but from what I just saw looking at the SRAM website you are right. Looks like the low end 9 speed chain is the PC 951, which is what I run on the applicable bikes.

IMO, it's worth the extra bucks to get the PC971. It has plating to resist rust. PC951 chains get rusty easily, in my experience at least.