As per the latest round of rumors, NVIDIA’s RTX 3080 (FE) may be as much as 35% faster than the Turing flagship, the RTX 2080 Ti, with the RTX 3090 being nearly 60% faster than the present fastest GPU. This info comes from reputed leaker kopite7kimi who has shared the 3DMark TimeSpy Extreme scores of the higher-end Ampere graphics cards, namely the RTX 3080 and 3090:

As you can see in the above chart, the RTX 3080 is around 30-35% faster than the RTX 2080 Ti while the 3090 is near about 60% faster than the latter. Although TimeSpy and FireStrike scores can indicate slightly higher than the actual gaming performance, this means that the RTX 3080 will be at least 25-30% faster than the RTX 2080 Ti, with the RTX 3090 being around 50% faster.
Considering this, you can be almost certain that the RTX 3080 will cost at least $799, with a $1,000 price tag not being completely out of the question. The RTX 3090, on the other hand, may as well cost between $1,499 and $1,999.
Considering that these chips will be fabbed on Samsung’s 8nm LPP node, they’re sure to run quite hot. As such, with the proper cooling, you should be able to extract another 10-1% performance out of the GPUs.