Ok, so finally got some resolution. I decided to keep the cards since I can't find 5870s for a reasonable price and I don't want to deal with shipping them back. BO is going to credit me with the difference in price.
Still though, this was very disappointing- I wanted the 70's. Also, they refused to answer how this happened- did someone else get my cards, did they sell more than they had in stock? If I didn't know what I was doing I could have been unaware that I didn't get what I ordered.