The other friends are right for that resolution you go with the 68xx family i was in 3Ghz and when i moved to 3.30Ghz i've seen +30 Fps more even i play the card in stock speed!? The problem is i have 65nm cpu and i can't go above i need 45nm CPU or 32nm CPU.
With 68xx you will have and more frames and less heat for sure is a 40nm GPU.
Here you can see a prime95 4096 minimal fft, 4Gbytes ram test and the furmark 1.8 extreme test but the HD5770 at stock speed:
http://admins.bnb.gr/~giatrakis/Prime95-toruture-4Gbytes-Furmak%20extreme-HD5770-stock.jpg
As you can see i see no difference in furmark with the stock speed in the card and the watts are not blown away! Only in some benchmarks I see some +2-10 Fps when I overclock the card but the temperature I get in stock speed is never above 63 C the cooling I have is very good. The near to 60 C in getting in 2 of the 4 cores is the highest and really big Temperature with NH-D14 cpu cooler. Above that I will damage the cpu once and for all, more volts to need it.
I mean a 45nm cpu and 32nm with the same cooling system never breaks the 40C is a must.
This ther idle after the test it took some time to cool it:
http://admins.bnb.gr/~giatrakis/idle-HD5770-stock.jpg
finaly the +10C i'm getting and the aditional watts HD5770 OCed woth it? I think you will agree is not.
HD5770 OCed :
AvP D3D11 Benchmark Report
==========================
**************************************************
* Report Created: 2010-11-09 @ 14:31:45
**************************************************
* Executable Build: V1.03, Apr 19 2010
**************************************************
*DX11 Hardware Detected*
Using Default Video Settings:
Resolution: 1280 x 1024
Texture Quality: 2
Shadow Quality: 3
Anisotropic Filtering: 16
SSAO: ON
Vertical Sync: OFF
DX11 Tessellation: ON
DX11 Advanced Shadows: ON
DX11 MSAA Samples: 1
Benchmark Summary:
Number of frames: 5041
Average Frame Time: 20.8ms
Average FPS: 48.1
HD5770 stock:
AvP D3D11 Benchmark Report
==========================
**************************************************
* Report Created: 2010-11-11 @ 15:22:59
**************************************************
* Executable Build: V1.03, Apr 19 2010
**************************************************
*DX11 Hardware Detected*
Using Default Video Settings:
Resolution: 1280 x 1024
Texture Quality: 2
Shadow Quality: 3
Anisotropic Filtering: 16
SSAO: ON
Vertical Sync: OFF
DX11 Tessellation: ON
DX11 Advanced Shadows: ON
DX11 MSAA Samples: 1
Benchmark Summary:
Number of frames: 4566
Average Frame Time: 23.0ms
Average FPS: 43.6
Use command-line option '-logframetime' to report performance frame-by-frame.
5 FPS only....