You haven't did your homework, have you?
Read the initial Anandtech's HD 5000 article. The GDDR5 controller used on HD 4000 was made without enough time to implement power saving futures. The controller on HD 5000 can downclock memory now. The ECC at low clocks can be disabled, too (no need for it) so the memory is similar too GDDR3 than and it's another power saving future.
Releasing cards on some gaming action do not look like proper release anyway. They'll finaly show some runing cards and real benches and than at some time the cards will arrive on stock. Usually there is 1-2 month between demoing the cards and releasing them![]()
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