SiSoft Sandra's benchmark database seems to be the place to be these days to find details about upcoming processors. Earlier today there was a leak about a 12-core Ryzen HEDT processor from AMD and VideoCardz also spotted some interesting details about the Intel Core i7-7740K. Most of the data matches an earlier leak from February.
The chip was benchmarked in the unreleased ASRock X299 Professional Gaming i7 motherboard, which uses the new X299 chipset to support Skylake-X and Kaby Lake-X. The board has a LGA2066 socket and the Core i7 7740K appears to be the very first Kaby Lake-X processor.
The benchmark listing reveals the CPU is a quad-core model with eight threads. It's clocked at 4.3GHz, it has a 4.5GHz Turbo, no IGP, and a 112W TDP. Memory support is reportedly limited to dual-channel as this appears to be a more budget class version of Intel's HEDT platform. Skylake-X will be where the flagships will end up, with six, eight and ten-core options, more PCIe lanes, and quad-channel DDR4 support.
It's not exactly sure when these chips will launch, last we heard they may not launch until Gamescom in August. VideoCardz compared the performance with some other chips, not sure how reliable the score of the 7740K is but it suggests multimedia performance comparable with the AMD Ryzen 7 1800X and CPU arithmetic performance comparable with the Ryzen 5 1600. Based on what we know today, it doesn't look too exciting and it's hard to see how much value this will add versus the 7700K.