According to a recently leaked slide, the upcoming Intel Core i9-10900K will be 2% to 30% faster than current Core i9-9900K. Intel Core i9-10900K is a 10-core and 20-thread Comet Lake-S CPU.
The i9-10900K and i9-9900K were reportedly tested with all security patches available on 4th November 2019. In benchmark such as Cinebench R15, the 10900K is up to 26% faster than 9900K. Based on all these results, the CPU is on average 13% faster than the current-gen CPU.