I borrowed this quote from a forum on moderns:
"A 520 chain has a roller width of 6.35mm, and the 530 has a roller width of 9.52mm, they both share the same pitch (distance between 2 pins)".
The B series all run a 520 as std, the A10's the wider 530, (havent checked what the A7's run) so a small weight penalty and the rollers still wear out.
a std 520 gives better chain clearance (being narrower) and is common to most modern high performance machines, so quite suitable for an A10 if both the sprockets being done. The 530 sprockets are wider.
I hope this makes sense...
With a 520 you also have room to run a heavier plate chain or even a power sapping X (the O is typically still too wide). I run a plain heavy plate 520 on the RR