It stays. CMOS stands for "Complementary Metal Oxide Semiconductor which acts a memory. Think of it this way. If you overclock too high your computer doesn't post each time you turn it on becuase it's trying to load the settings you put it at that are too high. Anyway point being, it's stays until you clear it or change it.
Yeah, for the D 820. I'm upgrading to Conroe regaurdless in August probably, but I was just curious in the meantime as I will probably OC the 2.4 Ghz one instead of paying so much for the 2.6. I was leaning towards Asus though.