did you make sure to delete your .bin file ?
sometimes you have to delete them for settings to actually take effect..
that is why a lot of people use a delete command in a .bat file.

such as this..


or


also verify you are using 100% GPU usage.. i use a desktop sensor panel i made with Aida64
or i sometimes use EVGA Precision or even better MSI Afterburner newest beta.
if you get anything under 100% usage something is not right then such as Intensity is set too low or other misc issues..
This can show you what is going on.. http://www.techpowerup.com/gpuz/

maybe check if these windows environmental variables exist too ?


not sure that makes any difference really but people always advise using those two variables
and they usually add them into their bat file too but you can enter them in manually.. they only have to be added one time.

experiment a bit with Intensity too.. you may find it works faster with lower settings.. my card hash's faster at 18 than it does 20 for example.

scan time 1 may not be a good idea for a pool either.. i am using 4 on my miners

edit:
i get a hair under 2.2mh/s on average on a Radeon 7950 which is a slower gfx card than the Radeon 280x
so any of you running a 280 you should be hashing faster than me

edit2:
i currently use amd_catalyst_13.11_betav9.5 (or 12.6 final)
they seem to be a bit quicker than newer ones
and both of those have the same opencl .dll's inside the installer so it won't matter too much speed wise i think which you use
but i found 13.12 final whql to be slower