Hi Tosca

I have the exact same setup as you and I have it get to working today
Make two different bat file

Mine is for the msi 290 card:

setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer --scrypt --verbose -o stratum+tcp://middlecoin.com:3333 -T -u 1PvWSTDzvbN89iedFLEyScP4j5qFgvVDPs -d 0 -w 512 -p x -I 20 --thread-concurrency 32765 --gpu-powertune 25 

Core clock 1000 memory clock 1499 this put out 875Khs and WU between 780-850

Radeon hd 5850:

set GPU_MAX_ALLOC_PERCENT 100
set GPU_USE_SYNC_OBJECTS 1
cgminer --scrypt -o stratum+tcp://middlecoin.com:3333 -u 1PvWSTDzvbN89iedFLEyScP4j5qFgvVDPs -T -p x -g 1 -d 1 -I 19 --thread-concurrency 5824

Core clock 765 memory clock 1000 this put out 330Khs and WU 275


Notice the different in -d this is for what gpu you chose

I have running this setup all day without any issue and it is great if you want to use the computer to surf just change the intensity in my case on 5850 I 19 to a lower number and you get out little less but can still use the computer, or just shutdown this card

Hope this will help you