https://www.theregister.co.uk/2018/07/20/intel_core_i9_performance_in_dell_apple_laptops/

Owners of laptops fitted with Intel's Core i9 high-performance chip, including models made by Apple and Dell, are finding that the machines slow down to the pace of older models.

Intel describes the six-core Core i9 as a "no compromises" chip aimed at gaming, VR and "next-level content creation". Intel has introduced a new feature intended for burst workloads, Thermal Velocity Boost (TVB), that adds 200Mhz of clock cycles to the standard 4.6Ghz of TurboBoost. Intel has said in briefings that TVB will run only if the processor temperature allows it to – below 50°C (122°F) – and that the processor speed may then drop in response to a temperature spike.