What do you do with your bike? Do you race? Stick w/ 530 because it's stronger if you just play or do stunts.
As for your chain, a good rule of thumb is when you switch sprockets switch your chain. Depending on how streached and worn your chain is now you may be fine. Leave your stock chain on if it fits and ride it.. when you have problems fix them..
Don't fix it unless it's broke. And personally I'm broke