Bit-Tech had an exclusive interview with David Kirk from NVIDIA about the clockspeed of the GeForce 7800 (G70). He confirmed that the new G70 chip uses multiple clockspeeds.
He says people claim the GeForce 7800 GTX doesn't have a new architecture, but that's not really true. It has a new architecture that isn't always visible. He stated that the G70 was designed from scratch to use less power by applying tricks they learned from developing mobile chips.
David explained the clock speeds within the GeForce 7800 are dynamic. The reporter asked what the three visible clocks did (ROP clock, pixel clock and geometry clock) but David replied that he shouldn't assume that there are only three clocks:
"The chip is large - it's 300m transistors. In terms of clock time, it's a long way across the chip, it makes sense for different parts of the chip to be doing things at different speeds."
The reason why NVIDIA didn't announce this as a feature was because they wanted the technology to speak for itself, according to NVIDIA's PR Manager Adam Foat. He says people noticed the effect (the quiet and cool operation) and that's exactly what they wanted.
One of the other reasons might be because NVIDIA didn't want ATI to find out about it and copy it.
NVIDIA also claims the GeForce 7800 should overclock better thanks to the multiple clocks that make the chip run cooler. They will also work together with the guys from RivaTuner to improve the program's overclocking features.