With the extra width the chain could wander side to side increasing the chance of derailling, also you would increase the contact pressure at the tooth/link interface thereby accelerating wear on the chain.
The intimate measurements (plate thickness-pin width-etc..) can vary from chain to chain, but any "5" series chain will have a pitch length of .625"
What windfall said about side-to-side is pretty much on. I don't know that you would experience much difference tooth/link interface wise though, as the pitch is exactly the same on both 520 and 530 chain.
What you will see is a chance of rubbing the case, and it will probably have a hard time at the chain guide. Not to mention more room for rocks and stuff.
Best bet is to use the correct chain for the correct sprocket set-up.