Looks like intel_pstate isn't able to change CPU's frequency (always max, also on powersave) when it's used in combination with CONFIG_NO_HZ_FULL (full tickless) on 3.10 rc2 (patched for ivy).
Can someone confirm?
Dirk Brandewie from intel sent me this workaround:
In General setup --> Timers subsystem unset Old Idle dynticks
And I can say that on 3.10 rc4 (the only kernel I tested on) it's working pretty well