Well, I thought I would run some tests to see if I could get more performance from this card.

First of all DO THIS AT YOUR OWN RISK, you have been warned…

My Test Scenario:
—-
AMD Radeo R9 200 Series
Specifically: R9 280x
OS: Ubuntu 14.04 LTS
cgminer version 3.7.2
cgminer intensity: 5
—-

First some setup if needed:

sudo amdconfig --initial --adapter=all
sudo reboot

How to update your clock and memory:

Enable overdrive, and set the clock.

amdconfig --od-enable
amdconfig --odsc=1000,1500

Where 1000 is the spot for you clock, and 1500 is the spot for your memory. These are the default settings for the R9 280x.

To check your current settings and temperature:

amdconfig --odgc --adapter=all
amdconfig --odgt --adapter=all

Hint: put commands above in a gpu_info script and have it watched, or put it in the startup:

watch ./gpu_info
gnome-terminal  --geometry=63x13+1140+40 -e 'watch ~/bin/gpu_info'

Here is how my test went:

Core Memory GH/s  Temp     Notes
---- ------ ----  ----     -----
1000 1500   1.127 69.00 C  Default Core/Memory
1000 500    1.127 71.00 C  Underclocked Memory
1050 500    1.183 71.00 C
1100 500    1.255 72.00 C
1150 500    1.300 73.00 C
1200 500    1.345 74.00 C  Last stable core clock
1250 500    ????? ???????  Slowed down, then GPU shut down

Now that I have a stable core clock of 1200, I will experiment with the
cgminer intensity. I would let it run for about 30 minutes or more to
make sure it really is stable.

Then save the settings:

aticonfig --odsc=1200,500
aticonfig --odcc

Here are my results when messing with cgminer intensity:

Core Memory GH/s Temp Load Intensity Notes
---- ------ ---- ---- ---- --------- -----
1200 500 1.514 77.00 C 95% d Dynamic intensity is the safest and where I keep it.
1200 500 1.412 76.00 C 90% 6
1200 500 1.487 76.00 C 94% 7
1200 500 1.512 77.00 C 95% 8
1200 500 1.545 77.00 C 97% 9
1200 500 1.565 77.00 C 98% 10
1200 500 1.576 77.00 C 99% 11
1200 500 1.582 77.00 C 99% 12
1200 500 1.585 77.00 C 99% 13
1200 500 1.587 77.00 C 99% 14 Fastest, but desktop may become sluggish.

So for me, I keep it at 1200 core clock, 500 memory clock, and intensity d. There are diminishing returns for increasing the intensity, but may be worth it for some people.