The standard PRS charger (came with the 500, optional accessory for the 505), also has a 2000mAh output, and it does, indeed charge something like 60% faster. If it were bad for it, I rather think Sony wouldn't have gone with that spec. The Sony folks are also the ones who gave us the idea of using a PSP charger in the first place.
The cable you're describing is a great option too.
