As Wayne says above, it's all about availability nowadays - a 630 setup is a bit harder to find and generally more expensive for no reason other than originality, if that's your thing. You will neither break, nor have an appreciably shorter service life from a smaller (530) set of chain and sprockets - you simply aren't dealing with large enough amounts of torque, HP or weight to warrant the larger chain and sprockets.
If you're really worried about (maybe) a couple of HP coming or going from a 40-odd HP bike that already weighs well over 200 kg, just make sure you have a decent bowel movement before every ride.
It will make more of a difference than most other things...
Last Edit: Jan 13, 2019 19:08:55 GMT -5 by pmcburney