A stock water cooled Intel Core i9-7900X can be run at 4.8GHz up from its normal 3.3GHz and run at 90°C / 194°F. However, if you want to take the risk you can pump it up to a whopping 5GHz.
Overclocker der8auer delidded the processor and replaced the stock TIM with liquid metal and combined the setup with a Corsair watercooler. He also suggests 4.9GHz might be possible without delidding the processor if you build a custom cooling solution.
The Intel Core i9-7900X is expected to retail for $999 when it releases later this year.
On the other side of the fence, AMD is going to be offering 6 more cores than the Intel Core i9-7900X, which has 10 cores and 20 threads, with the AMD Threadripper which has 16 cores and 32 threads. Best part of that is that AMD is rumoured to be charging almost $150 less for their top end chip compared to Intel.