My laptop, Medion Erazer 7842, which is a branded Clevo Barebone P671RG, has an i7-6700HQ and SST is disabled as per HWinfo on Windows 10 10586.
I also checked the ACPI FADT PreferredPowerManagementProfile and according to
http://wiki.osdev.org/FADT#PreferredPowerManagementProfile it is set to Mobile (0x02).
So I guess the mobile/desktop theory is busted.
But then I tried booting Linux with the parameter you provided. It booted but I had no way of confirming it actually worked. So I did some googling and I found this:
https://bugzilla.kernel.org/show_bug.cgi?id=110941. Apparently there was some trouble supporting HWP in the old kernels. But it provided the information where to check if HWP is running.
It mentions cheking MSR register 0x770. So after booting with intel_pstate=skylake_hwp, MSR 0x770 showed 1. So it appears it has worked and HWP got enabled under Linux. It also mentions that to enable HWP you have to write 1 to that register.
But then I thought: what would happen if I wrote 1 to MSR 0x770 from windows? So I fired up RWEveryhting and did it (for all cpus). It worked!
Hwinfo shows SST enabled. Now I tried setting the windows power profile to Powersave. This ussualy means very slugish frequency changes and a very noticable drop in responsivness. CPU still ramps up very quickly and the system is very responsive. It appears to completely ignore all windows settings (including maximum frequency in the power options). So it appears SST really does work.
There appear to be no other side effects and I'm writing from my now SST enabled laptop. Also I think it should go without saying, but messing with MSR should be done at your own risk.