Someone with access to the upcoming Intel Core i5-9600K has run it through GeekBench 4. The chip was able to score 6015 point in the single-core test. This is about 3.7% faster than its predecessor (Core i5-8600K). This is thanks to the 300 MHz higher single-core boost. The multi-core score was 23,939 points, which is only 2% faster than the i5-8600K.
It seems the jump in the performance for the mid-range has really stagnated. The Core i5-9600K will really only fix the price / performance situation the i5-8600K has against the AMD Ryzen 5 2600X.
The Core i5-9600K is a 6-core, 6-thread part that will have a base clock of 3.70 GHz and will boost up to 4.60 GHz. It should hit the $250 price-point area.