it's probably because guiminer is set to mine sha256 and not scrypt, the other one sgminer is indicating the correct value
if you can tell me what amd card do you have, then i could help you with intensity, usually for 280x you need 13, which is the best spot, and for 290/290x it's better to rise it to 19-20
Oh I see, I'll try to set it to scrypt and see what it says!
EDIT: I don't see any settings to switch from sha256 to scrypt, any idea?
Thanks for your reply, I have a Gigabyte AMD Radeon R9 280x right now.