Controlling AMD GPU Core/Mem frequencies and voltages for power usage minimization

[twotimes]

I've been playing around with my setup (3770k - gigabyte z77x-ud5h - Sapphire 7970 with GOP-capable bios), dual booting between OSX (Mavericks/Yosemite) and Windows 8.1. I noticed that the power consumption measured at-the-wall is lower for Windows 8.1.

I blame it mainly on inflexible clock/voltage management of the AMD 7970 GPU under OSX.

Below are some numbers.

OSX idle power use:
dual display setup, HDMI+DVI - 105 W
single display setup, HDMI only - 71W

Win 8.1 idle power use:
dual display setup, HDMI+DVI - 79 W (vCore=0.95V, CoreFreq=300MhZ, MemFreq=450MhZ)
single display setup, HDMI only - 61W (vCore=0.85V, CoreFreq=300MhZ, MemFreq=150MhZ)

In Windows 8.1 I can monitor/control GPU core and memory clock frequencies and voltages with tools like MSI Afterburner and Catalyst Control Center.

Seems like the idle clock used by OSX are the default max values defined by vBios (1050MhZ core/1500MhZ mem).

Is there any way to monitor/change the clock and voltage values under OSX for AMD GPUs?