It was related with drivers first time I saw that on a pc. Try with 13.1 or 13.2 catalyst drivers.

Maybe you'll need to unistall current ones for better result. Try standar clocks to guess if your card is runnung well, an after that test with overclock to no mixing problems.

Hey, it solved to me a problem I though it was related with drivers for mixing cards.. did not noticed about this, thanks!

For the 7850 that I've tested, more than 300 are achievable... try to test differente combinations of threadconcurrency and raise a little intensity.
And for the computer freeze... not sure its realted at all with bad settings even if now they are a bit low.. maybe its a different problem of power or temperature of the card or computer.

Hi,

For the part of overheating.. try to monitor your temps of your gpu, imo safe temp should be less than 70 ºC if you plan 24/7... I recommend for this to download msi afterburner, so you can also program fan rpms with the temperature.

For the other parts, I've not tried still solo mining...