Bike Forums - Chain size 8 spd vs. 9 spd

Please forgive me if this has been posted before. I did use the search function, but got no answers.

I have a Cannondale F300 which has an 8 spd Sram drive train including SX4 shifters, and SX5 rear dérailleur. I don't like the shifters because they have a lot of loose travel, and both up and down shifting is done by moving the same lever. I found a set of X5 shifters and an X5 rear dérailleur on eBay for $30 (pretty good deal I'd say). They are both 9 spd, which means I'll need to change out my cassette, which is no problem.

The question I have is whether I will need to swap my chain as well. I understand that 9 spd chains are narrower than 8 spd to accommodate the closer spacing of the cassette cogs, but is this difference large enough to really be a problem? If I run an 8 spd chain on a 9 spd cassette, will it bind, not shift properly, or cause damage to my cassette? Or is the difference negligible?

On a side note, what is the difference between Sram's SX5 and X5 components? I can't find anything to explain it, so I'm considering keeping my SX5 rear dérailleur on my bike to avoid the hassle of hanging and adjusting the new one, and keep the X5 as a spare.