GTX 670 & i5 3750k - Low framerates on Unigine DX11 Heaven

Hey everyone,
Just got a new PC running and I'm just wondering why I'm getting a low score on the DX 11 Unigine Heaven demo? Not trying to be knit picky or anything, as my other games are running real solid, The Witcher 2, Diablo III, SC II, Assassins Creed III run at 60+ at max settings w/ 1080p. I haven't overclocked or tweaked anything since I have my stock Intel fan on my CPU. So here are some results I gathered from the demo.

Heaven: AS 16x/AA 8x, Extreme Tesselation, 1080p
FPS: 32.5  
Scores: 815
Min FPS: 10.4
Max FPS: 60.8

Heaven: AS 8x/AA 4x, Extreme Tesselation, 1080p
FPS: 38.1
Scores: 960
Min FPS: 21
Max FPS: 62.4

Heaven: AS 8x/AA 4x, Normal Tesselation, 1080p
FPS: 53  
Scores: 1336
Min FPS: 21.3
Max FPS: 65.4

The reason I'm posting this up is because I've seen people with similar builds as my own rock this test at Extreme Tesselation w/ 16x/8x, 1080p. Could there be something wrong w/ my CPU? I hear all this talk about bottlenecking with no clue as to what it is. My GPU temp under full load gets to 58c max, CPU temp reaches upper 40's. What I do notice is that when running the heaven demo in windowed mode, my task manager shows my CPU speed fluctuate alot, from 1.5ghz - 3.5ghz, hitting anything in between too. Could this also be a Windows 8 issue? All similar builds I've seen had Windows 7 64 bit. Thanks a bunch.

Here are my Specs:
Windows 8 64 bit
MSI Z77a-G45 Mobo (latest Bios 2.70)
Corsair Vengeance 8gb (2x 4gb @ 1600mhz)
Intel i5 3570k @ 3.4 ghz
Gigabye GTX 670 2gb (OC version w/ Windforce 3x fans)