All non-K/X CPUs have locked multiplier, except for the Pentium G3258 "25th Anniversary" edition.
Skylake CPUs can be overclocked by a significant amount through base clock modification since the CPU/RAM has a separate base clock from IOs. In older Intel CPUs though, there is only one reference clock for everything and USB/PCIe does not overclock by more than about 5%, making BCLK overclocking largely pointless