Effective clock speed.
It has become a common practice for several years to report instant (discrete) clock values for CPUs. This method is based on knowledge of the actual bus clock (BCLK) and sampling of core ratios at specific time points. The resulting clock is then a simple result of ratio * BCLK. Such approach...
www.hwinfo.com
Prime95 Small FFT forces 100% steady state load on all cores. Gaming does not. Gaming is going to be highly variable depending on the specific game and how it has been optimized, or not optimized, for single and multithreaded performance. And I think you mean "efficiency cores" not "effective cores". As far as "enhanced boost", that is simply an automatic overclock configured by MSI and if you don't have really good cooling then you might be seeing lower clock speeds because the system is throttling due to temperature issues.
I'd recommend NOT using any automatic overclocking features like enhanced boost and simply use the default configuration for your CPU which would include Intel speed step and Intel speed shift being both enabled, or disabling Intel speed shift and only leaving Intel speed step enabled. And leaving the setting for the default boost profile enabled. So, turbo boost enabled, hyperthreading enabled and speed step and speed shift (Or at least Intel speed step) enabled.
Or simply reset the BIOS to the factory defaults and then leave it as is aside from configuring any personal settings that need to be configured such as fan curves, etc. More often than not, especially if you don't have really exceptional cooling all the way around including for the CPU and case, those automatic overclocking profiles and such end up hurting more than helping.
Knowing your full hardware specifications would also be helpful.