520 refers to the sprocket/chain thickness. with a thinner chain/sprocket combo, there will be less rotating mass, and in most cases you will see a small gain in power.
But when you gear it differently, i.e. -1 in the front and +2 in the back, the bike accelerates quite a bit faster and takes away from the top speed. (which you should know) this is why stunters go up alot in the rear, for low end power.
brand will make a difference, stick with the big guys and you shouldn’t have a problem. If you really need to replace the chain, sprockets don’t add much to the cost, so you might as well make a difference on the bike. BUT if you get a 520 chain, you need 520 sprockets. and vice versa.