Most likly just updated versions of the current cards.
A bit faster clockspeeds. possibly more memory.
Updated support for things like SM3 on the ATI side.
I think they will be relative to the gap between a 9700 and a 9800.
In short.... No.
As long as its compatible ram the manufacturer doesnt matter to much.
Most likley its just marketing....trying to get you to buy a certain brand.
Like if you buy laundry detergent....."be sure to use X brand stain remover for best results".....Its BS.