Just in case anybody is interested:
I called EVGA and spoke to one of their techs tonight. Very nice fella! Anyway, he has clarified this for all of us:
All 4 7800gs cards that they offer are at 1.4ns memeory response time. The 1.6ns was a typo.
Also, three out of the four cards state that they have CINEFX 4.0 and INTELLISAMPLE 4.0. The 7800 GS CO states it has 3.0 versions of these. This is also a typo. All four cards have the 4.0 verisons.
The other thing he clarified is that the 3 cards with "CO" in the model title have better copper heatsinks, while the bottom of the line 7800gs (model N505) does not.
There you go! So in conclusion and to affirm what a lot of people have told me, buy the 7800gs CO (model # N506) with the evga fan (got mine for $299 with free shipping from circuit city) and overclock it yourself and save the dough!!!!
Thanks to everyone for their advice and help on this!