Overclocking an ATI radeon 5870

[jkphotoguy]

Hey guys I have been finding when I over clock My GPU (ATI Radeon 5870) that it increases the FPS of my games a bit but the more and more I push the graphic card the slower it gets. for example I was running a benchmark on one of my games and with the cards default clock (850 MHz GPU clock & 1200 MHz memory clock) my best was 71 fps. I overclocked my GPU to "890MHz GPU clock & 1205 memory clock" and with the same test only scored 31 fps at the best. I thought that doing a bigger overclock would make the GPU work faster please help.

jkphotoguy

 

[Apokalipse]

The 5870 has a couplle of features which will cause this to happen

first, the memory uses ECC. That means that it keeps checking the memory for errors.
If an error occurs in memory (which might happen when you overclock it), it fixes the error. But that makes it slower.

Second, the it monitors the power going through the card. If too much power is going through the card (which can occur if you've overclocked/overvolted it and are stressing the core to extreme levels, such as using Furmark or OCCT), it will drop down to a lower power state (usually 400MHz core, at 1.0625V) to avoid damage to the card. I'm guessing this is most likely what's happening in your case.

What I've done with my 5870 is modify the BIOS to change the stock volts to 1.175V in performance mode (default is 1.1625V), and set the stock speed to 950MHz
I also increased the clock limits to 1300MHz core, 1500MHz memory. So Catalyst Control Center will allow you to set the speeds up to those levels (not that I'm likely to).
I've uploaded it here:
http://sites.google.com/site/apokalipse/5870mod.rom

Also, it's much more reliable to flash the BIOS using DOS + atiflash
You would use:
atiflash -p -f 0 5870mod.rom