Hardware Canucks posted a review on the Sapphire HD 4890 1GB video card

Enter the brand new HD 4890 1GB, a card that builds upon the HD 4870 with increased clock speeds under its belt and supposedly bucket loads of overclocking potential. Essentially, this is exactly what the name suggests: an overclocked HD 4870 with the new designation of RV790. This sticks quite well with what we mentioned about modified versions of existing technologies being used to cement a company's place in the market. Indeed, it seems like ATI has really hit its stride with their current 55nm cores and they are making good use of them once again.

Sapphire HD 4890 1GB Review