suddently dropped hashrate in litecoin mining

[vvic]

Ok, guys/gals I have a question. Still new to all this mining stuff, so...  I've been mining litecoins for a while now
I have radeon 7970 and 6770 and bunch of CPU miners (around 30khash/s)
Not sure what happened ddos or what, but miners wouldn't connect to pool-x or ozco.in. When i finally was able to connect, every miner would have like 95% off stale shares
after while and working with cgminer settings, (cgminer --scrypt --worksize 256 --shaders 1792  --lookup-gap 2 -g 1 --thread-concurrency 8000 --intensity 13 -o http://pool:9332 -u xxxx.x -p xxx ) I got stale around 10% but speed dropped significantly. Before I had 530khash/sec on my 7970 now I have like 490 and different settings wont bring it up (just makes more stale shares) and while my speed overall is dropped, suddenly I see pool-x users get crazy hashrates, like 12700khash and ozco.in is even more. So... two questions:
Does anybody know what do they use? Asics or something?  and what settings could I use to improve my speed? I've tried various of different options for cgminer, but only get more stale.
Thanks

[chondrite]

I have found that the only setting I need to change in cgminer is the "intensity" level.  Cgminer seems to find the max values for my other settings(except clock values).  Usually when I try different settings than default I get heavy stales or hw errors. 

Users with high hash rates have multiple GPU/CPUs running.   So someone with 12700 Khash probably has several dozen different units running.

[bushstar]

Normally when I start getting lower hash rates it is due to heat. These cards do not make it six months without an air dusting. Get an air duster, take the cards out and make sure that the heat sink is free from dust. One of my mining rigs went from 1200Kh last week to 900Kh because one of the cards was hitting 85C. With an air dust and increased fan speed they are running full speed again at 77C.

For a 7970 I have the following set which is not much different from your setup.

"scrypt" : true,
"kernel" : "scrypt",
"kernel-path" : "/usr/local/bin",
"intensity" : "13",
"vectors" : "1",
"worksize" : "256",
"shaders" : "2048",
"gpu-threads" : "1",
"thread-concurrency" : "8192",
"lookup-gap" : "2",
"queue" : "3"

With this I get 550Kh stock and 600Kh at 1125/1650 GPU/RAM.

[vvic]

ohh!! this is very great point! Thanks, guys. I will check tonight dust and heat