Hi Brian - from what I've read so far there isn't an established RDA for Omenga-3. From the information you yourself provided, the International Cod Liver Omega-3 Foundation have suggested a Healthy Daily Intake (HDI) of 450mg (http://www.clo3.com/sources_equal/so...qual_index.php).
I can't say what the benefits / costs are to the human body of taking more than this, only that it seems to be agreed accross the board that this is a sufficient and significant amount.
Krakers.