Higher FPS when underclocking - 7870 LE - Why?

[TurboFiend]

Hi

Windows 7 Ultimate 64-bit SP1
Intel Core i5 2500K @ 3.30GHz
8.00GB Dual-Channel DDR3 @ 665MHz (9-9-9-24)
MSI P67A-G45 (
VW246 (1920x1080@60Hz)
PowerColor PCS+ Radeon HD 7870 (Tahiti LE) 2GB Myst
112GB OCZ VERTEX2 SSD
112GB Corsair Force 3 SSD
750W Powercool PSU

I've just been overclocking the core clock on my 7870 Tahiti LE GPU but it seems it doesn't give it higher FPS. In fact in some benchmarks it gets higher FPS when it is underclocked

I've been overclocking with Catalyst Control Center and verifying in GPU-Z. GPU-Z says the core clock is underclocking (stepping down?) when I overclock the GPU and run it, going between the overclocked amount (1100) and something lower (usually about 500) about half the time. The temperatures are fine, I've tested it with furmark and it stays around 65C, definitley not overheating.

Here are my results, (I've bolded the highest FPS);

Uniginge Heaven Benchmark 4.0

DX 11
Quality: UItra
Tesselation: Normal
AA: x4
Resolution: 1920x1080

Core clock: 1100
Average FPS: 24.6
Score: 620

Core clock: 975 (default)
Average FPS: 27.4
Score: 620

Core clock: 800
Average FPS: 29.5
Score: 744

Core clock: 775
Average FPS: 31.0
Score: 780

Total war: Shogun 2
1080p DX11

Core clock: 1100
Average FPS: 42.45

Core clock: 975 (default)
Average FPS: 57.375

Core clock: 800
Average FPS: 54.2

Core clock: 775
Average FPS: 52.775

Metro 2033

DX11
1920x1080
Quality: Medium
AA: MSAA 4x
AF: 4x

Core clock: 1100
Average FPS: 44.33
Min FPS: 8.55
Max FPS: 242.42

Core clock: 975 (defualt)
Average FPS: 46.33
Min FPS: 10.18
Max FPS: 304.79

Core clock: 800
Average FPS: 47.67
Min FPS: 4.90
Max FPS: 273.82

Core clock: 775
Average FPS: 49.33
Min FPS: 8.45
Max FPS: 239.29

Core clock: 700
Average FPS: 50.00
Min FPS: 8.05
Max FPS: 260.21

Also when I was mining Litecoins about a year ago I got the best hashrate at 755 coreclock. I thought it was a quirk of the mining algorithm, apparently it is like that for other things aswell.

Anyone have any ideas about what I should do?

 

[TurboFiend]

I flashed the GPU BIOS to a newer version, now GPU-Z reads the correct values of the overclock settings, both overclock and under clock, and it doesn't down clock the GPU when it is under load.

I was following this thread (I reccomend you read it all as it contains links to different versions of the BIOS); http://hardforum.com/showthread.php?t=1750373

I still get a minutely lower score in the Heaven benchmark running at 1100 on the new BIOS compared to 775 on the old BIOS (30.7 FPS vs 31.0 FPS respectively). At 775 the new BIOS showed 32.1 FPS compared to 31.0 on the old BIOS.
On Shogun 2 I got a slightly higher score at 1100 on the new BIOS compared to the highest scoring setting, default 975 core clock, on the old BIOS (59.1875 FPS vs 57.375 FPS respectively).
In Metro 2033 I got 47.67 average FPS with the new BIOS compared to 44.33 on the old BIOS at 1100 core clock. I got a lower FPS at 700 compared to the old BIOS, 50.00 for the old and 48.33 for the new.

I'm still puzzled as to why I still get higher FPS when it is underclocked, anyone got a suggestion?

 

[TurboFiend]

I've tried overclcoking my CPU from 3.3Ghz to 4.4Ghz. It has increased the frame rates but I am still getting higher FPS in some games with lower clock speed on my GPU.