Bigsexy, most people will tell you (non-technically) that Nature relies heavily on your memory. Relaxed timings on your memory will return lower scores in Nature, while lower memory timings will give you higher framerates. At 1.8GHz (180x10) I can only run my memory at 2.5-3-3-6, and I get about 30FPS. At 1.75GHz (167x10.5) I can run 2-2-2-6, and my FPS go up to around 50.
Do a re-install, in the following order:
Clock down to stock speeds, and install Windows (minimum install, no language packs, networking, etc...just the basic files).
Install the drivers for you motherboard. Reboot.
Install the video drivers. Reboot.
Install 3DMark. Apply your CoolBits hack, and Reboot.
Boot into Safe Mode and defragment your HDD.
Clock back up as high as you can while keeping your memory timings as low as possible.
Reboot, set your D3D at Best performance, uncheck Enable Fog Table emulation, and set VSync to Always off. In OpenGL, check Use fast linear-mipmap-linear filtering, and set VSync to Always off again. Set your clk/mem to whatever you know is stable. Run any other tweaks you want to at this time.
CTRL/ALT/DEL, and kill any process that doesn't need to be running.
Run 3DMark.
Post your scores.