No, it is not. The HD5550 is weaker than the HD4670. The equivalent of the HD4670 for the new series is the HD5570. They have similar performance overall but the HD5570s benchmarks are more inconsistent, significantly better in some games, worse in others. See if you can convince them to give you an HD5670 for the trouble you are going through because they sold you a card that wasn't as advertised and then tried to replace it with a weaker card.
As for the initial problem however it is not really one. The HD4670 cannot effectively use more than 512mb of ram, the 1gb versions are really just a marketing gimmick(or worse if they use DDR2 ram instead of DDR3 which actually will affect performance.)
Well I paid a lot for it, problem with buying locally. 93.00+tax
it is a HIS with their cooler (3slots) and the box says DDR3, it is in fact the HIS brand just a 512 mb version instead.
Maybe I should just ask to get it for less money. I figure to ask for the 5670 or 9800GT as comparable replacements.
Thanks for your reply.