Found this in a post from 2007;
530 X-Ring chain and 630 O-Ring chain are virtually the same width - they both use 3/8 wide rollers (that's the 30 in the 530 and 630 - that means 3/8" width for the rollers).
Spacing isn't an issue provided you install a spacer washer on the front sprocket.
The benefits for 530 over 630 are considerable - cheaper, better selection, better wearing, and lighter. The cons - really none - except for a couple of bikes where there isn't a readily available 530 rear sprocket (KZ900 LTD uses a unique rear sprocket - so no 530 rears are readily avialable).