What intensity and concurrent threads are you running? Also what is the temp of the gpu under load?
I had an issue with scrypt mining on one of the rigs that had 3 7950. I had 4 gig ram and once I upgraded to 6 all gpu were running full speed. I am not sure if that is the same issue as you are having. You can try and it and see if it works.
How much ram does the system have?
Question: I'm hashing with two R9-290 with the guiminer scrypt. The first one (connected with monitor) reaches 840 khs the second without connection to a monitor got only 660 khs. Is that normal?
I'm using the same guiminer settings for both GPU's. Installed catalyst and and SDK only before using the first card. Used to second card just today.
8GB
I see this as well but i am running two 280x with gpu capping at 550 khs while gpu 1 can almost do 700 khs on GRC. changing intensity seems to make it worse. I have 8 gb ram installed. i am wondering if gp0 is hindered by windows. i am not a linux guru so all my xp in mining has been windows. also, i am a newb.