If you're thinking of upgrading, new Intel CPUs....

[DaddyAce]

....are out, and just starting to be available for sale.   My puter engineer son was originally skeptical, but now that they are out seems pretty impressed with this new line of processors.  They seem like they may offer impressive gains, and hopefully should soon drive down prices on the Kaby Lake series.  Tom's Hardware has a nice review and discussion, focusing mainly on the new flagship gaming  i7 8700K, but also has info on others in the series:  http://www.tomshardware.com/reviews/intel-coffee-lake-i7-8700k-cpu,5252.html

[Denniss]

Be aware that some test may be flawed due to buggy Bios, permitting far higher wattages for the CPU than specified by Intel resulting in higher sustained (boost) clockrates.
At least certain asus mainboards are affected. May explain the performance oddities THG noted with the 8700 and its too high performance compared to 8700k

[Skuzzy]

Boost clock rates should be negatively impacted, by higher watts, as part of what drives the boost clock down is heat.

The boost rates are difficult to control as they are driven by heat and CPU loads.  In a Windows 10 environment it is difficult to control exactly what a CPU may be doing, at any given point in time.

About the only way to track the boost rate would be to track the number of threads actually running when testing along with the thermal load.

[Denniss]

heat dissipation may be improved in the six-core coffee lake thus they were not easily running into thermal limits with their single-core boost applied to all cores, at least the 8700 using lower standard voltages. The 8700k operates with slightly voltages and may have been affected by thermal limits in certain THG test where the 8700 was faster than 8700k.
We'll all know better once the sites update their tests with fixed Bios adhering to proper TDP and boost limits (and with automatic overclocking disabled in Bios for a fair comparison)

[Denniss]

https://www.gamersnexus.net/guides/3077-explaining-coffee-lake-turbo-8700k-8600k
http://www.hardware.fr/articles/970-17/attention-aux-overclockings-automatiques.html

further question is how high these board clock the uncore area of the CPU (mem controller, L3 cache). if they are raised above specification this will influence performance a lot.
Really nebulous what's the real CPU performance of Cfl at stock/specified speed without auto-overclocking/-volting and TDP exceeding.