It looks like Sapphire has struck gold with their HD 4890 Toxic Vapor-X. The card offers considerably improved performance over the HD 4890 reference design and can beat the GeForce GTX 280. It does all that without being noisy, it is much quieter than all other HD 4890 cards I tested so far. It's great that Sapphire finally listened to our constant nagging: "your cards are too noisy". Another plus is that Sapphire has gone with the reference design voltage regulators which means that the card supports voltage control via software for GPU core and memory voltage. Personally I am not sure if there is a gain from going PCI-E 8+6 voltage connectors from 6+6 but it certainly won't hurt.
The only thing that I can complain about is that the overclocking potential beyond Sapphire's stock clocks is very limited - we saw only about 1%. However, since Sapphire's card runs at 1.4V, you can up the voltage to 1.5V safely, then you should be able to reach 1 GHz on the core.