Since I can't post in the official thread, I will post the problem here.

I am mining 2 6990s on xp sp3(SDK2.4 Cat 11.6) with crossfire enabled because I can't see the gpus when disabled.
I have been mining for just over a week. The reason I'm using diablo is because that old version is the only miner that i tried that could use all 4 of my gpus.
There are several problems, some of which I'm sure are limited to other factors. But here are all of them.

5-10% rejected shares
 The rejected shares are rarely isolated, but group together with usually 5-20 rejected all at once on all gpus, which indicates there's some type of flaw in the miner, since i got only as high as 1.5% on phoenix.
need to use old version of diablominer since new version only gives me 50-75% of the rate with a very huge rate of hardware errors.
 On the most recent version
frequent disconnects on pools and errors about longpolling too frequently.
speeds are not stable and fluctuate by as much as 10%

The biggest problem is the hardware errors, reduced speeds, and stales. Diablo or experts please help.