litecoin 5870 & 7850 cgminer settings

hi,

as the title suggests i have some problems with 2 of my cards.

XFX 5870 1GB
On the 5870 intensity 9 - 13 works but gets 260 k max if i go higher i almost only get HW errors hashrate goes up to max 310.
But if i change the thread concurrency to anything above 5000 i get no errors but my hashrate drops to around 280 kh no matter what settings i try it just stays at 280
any suggestions?

MSI R7850-1GD5/OC
The 7850 is a different story i can get 280 kh:

Code:

./cgminer --scrypt --thread-concurrency 5120 -I 12 --gpu-engine 900 --gpu-memclock 1200 -w 256

But it hangs between 1 and 2 hours with other settings i can get higher hashrates but it hangs within 20 min. (hangs as in cgminer needs restart but sometimes it cant find card after restart)
Is the card fried?

I tested both cards on seperatly on a asus P8H77-V LE with 8Gb memory and 450w power running Xubuntu.

thanks!