Here is a before and after on 4x 6870. Everything worked as advertised! Using xfx reference cards.
C:\ct>clocktweak.exe -x
===============================================================================
ClockTweak v0.9.0b - bitcoinX.com/clocktweak/
===============================================================================
ERR: ADL API function: ADL_Display_PossibleMode_WinXP_Get is missing.
Exploring up to 20 adapters:
A.#:0 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:0
A.#:1 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:0
A.#:2 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:0
A.#:3 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:0
A.#:4 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:1
A.#:5 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:1
A.#:6 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:1
A.#:7 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:1
A.#:8 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:2
A.#:9 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:2
A.#:10 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:2
A.#:11 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:2
A.#:12 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:3
A.#:13 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:3
A.#:14 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:3
A.#:15 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:3
A.#:16 r:-1 explore_adapters: adapter 16 could not be initialized
A.#:17 r:-1 explore_adapters: adapter 17 could not be initialized
A.#:18 r:-1 explore_adapters: adapter 18 could not be initialized
A.#:19 r:-1 explore_adapters: adapter 19 could not be initialized
valid adapters: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
gpuAdapters: [0, 4, 8, 12]
Reading data:
#0: Temp:43 Load:17 Fan:21 CoreL2:900 MemL2:1050 mVoltL2:1175
#4: Temp:43 Load: 0 Fan:21 CoreL2:900 MemL2:1050 mVoltL2:1175
#8: Temp:44 Load: 0 Fan:23 CoreL2:900 MemL2:1050 mVoltL2:1175
#12: Temp:41 Load: 0 Fan:22 CoreL2:900 MemL2:1050 mVoltL2:1175
C:\ct>clocktweak.exe -a all -c1000 -m300 -v1000 -s95 -y
===============================================================================
ClockTweak v0.9.0b - bitcoinX.com/clocktweak/
===============================================================================
ERR: ADL API function: ADL_Display_PossibleMode_WinXP_Get is missing.
Set values - starting.
Adapter #0:
setting core speed to 1000 [MHz]
setting mem speed to 300 [MHz]
setting voltage to 1000 [mV]
setting fan speed to 95%
Adapter #4:
setting core speed to 1000 [MHz]
setting mem speed to 300 [MHz]
setting voltage to 1000 [mV]
setting fan speed to 95%
Adapter #8:
setting core speed to 1000 [MHz]
setting mem speed to 300 [MHz]
setting voltage to 1000 [mV]
setting fan speed to 95%
Adapter #12:
setting core speed to 1000 [MHz]
setting mem speed to 300 [MHz]
setting voltage to 1000 [mV]
setting fan speed to 95%
Set values - finished.
Reading:
#0: Temp:42 Load:16 Fan:55 CoreL2:1000 MemL2:300 mVoltL2:1000
#4: Temp:42 Load: 0 Fan:46 CoreL2:1000 MemL2:300 mVoltL2:1000
#8: Temp:43 Load: 0 Fan:40 CoreL2:1000 MemL2:300 mVoltL2:1000
#12: Temp:41 Load: 0 Fan:23 CoreL2:1000 MemL2:300 mVoltL2:1000
c:\ct>clocktweak.exe -x
===============================================================================
ClockTweak v0.9.0b - bitcoinX.com/clocktweak/
===============================================================================
ERR: ADL API function: ADL_Display_PossibleMode_WinXP_Get is missing.
Exploring up to 20 adapters:
A.#:0 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:0
A.#:1 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:0
A.#:2 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:0
A.#:3 r:0 ID:10633280 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:0
A.#:4 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:1
A.#:5 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:1
A.#:6 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:1
A.#:7 r:0 ID:17062784 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:1
A.#:8 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:2
A.#:9 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:2
A.#:10 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:2
A.#:11 r:0 ID:100407360 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:2
A.#:12 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:1 GPU:3
A.#:13 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:3
A.#:14 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:3
A.#:15 r:0 ID:18778432 Name:"AMD Radeon HD 6800 Series" Active:0 GPU:3
A.#:16 r:-1 explore_adapters: adapter 16 could not be initialized
A.#:17 r:-1 explore_adapters: adapter 17 could not be initialized
A.#:18 r:-1 explore_adapters: adapter 18 could not be initialized
A.#:19 r:-1 explore_adapters: adapter 19 could not be initialized
valid adapters: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
gpuAdapters: [0, 4, 8, 12]
Reading data:
#0: Temp:38 Load: 0 Fan:97 CoreL2:1000 MemL2:300 mVoltL2:1000
#4: Temp:37 Load: 0 Fan:96 CoreL2:1000 MemL2:300 mVoltL2:1000
#8: Temp:38 Load: 0 Fan:97 CoreL2:1000 MemL2:300 mVoltL2:1000
#12: Temp:36 Load: 0 Fan:94 CoreL2:1000 MemL2:300 mVoltL2:1000