Intel Corp (INTC)

[chipguy]

Interesting that Broadwell-C/H never made it to particularly high frequencies either; lower than their 22-nanometer Haswell counterparts actually (Intel ships 4GHz turbo HSW chips for laptops and 4.4ghz turbo for the 4790k; BDW-H tops out at 3.7GHz-ish IIRC).

I definitely think it's a process-related problem.

Why?

Intel has been dialling down TDP while increasing the proportion of
area and power budget dedicated to integrated graphics. Desktop no
longer drives core design, mobile does. Generally speaking increasing
power efficiency at 2-3 GHz reduces headroom for operating above 4
GHz. That is a conscious business decision by Intel. With no effective
competition from AMD all overclockers can do is cry in their beer.