On a few of my rigs using any miner after 3.4, I get constant crashes and machine hangs which is a PITA as I have to drive to my location to restart them.
I've ran a lot of tests, clocks set to stock, over and underclocked and I get constant machine lockups after a few hours. The worst rigs are my 6x tri-x 290'with the machine hang issue, I have a few 4x 7950 rigs as well and get a lockup on a couple of those. Logs on all are similar to the following:
18:59:33:839 5c8 watchdog - thread 0, hb time 1965
18:59:33:839 c68 Round
18:59:33:849 5c8 WATCHDOG: Thread 0 hangs in OpenCL call, exit
18:59:33:859 5c8 watchdog - thread 1, hb time 671
18:59:33:859 5c8 watchdog - thread 2, hb time 1950
18:59:33:859 5c8 watchdog - thread 3, hb time 0
18:59:33:859 5c8 watchdog - thread 4, hb time 234
18:59:33:859 5c8 watchdog - thread 5, hb time 0
18:59:33:849 f00 Time gpu (2): 1950563
18:59:33:869 5c8 Restarting OK, exit...
It looks like the miner app restarts a couple of times as there are a couple of additional logs files that are just 1kb in size with only the following in:
19:01:34:659 b2c
19:01:34:739 b2c ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
19:01:34:739 b2c º Claymore CryptoNote GPU Miner v6.1 Beta º
19:01:34:739 b2c ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ
It then hangs the system but there is very little info in the event viewer as to why. Once this happens the machine drops off the network and I have to reset it to get it going again.
Something a bit odd with my 290 rigs, if I actually downclock the core/mem to 947/1250, I get a faster hashrate...? at stock and any overclock I get under 3900, but down clocking the cards results in a higher hashrate. Bit odd. I see no hashrate increases by adjusting mem, only changes to the core appear to have an effect on hashrate.

It doesn't work with my 7950 rigs, but I'll take lower power usage from the 6 card rigs any day.
I'm running 13.12 drivers with LBR's mod from
https://litecointalk.org/index.php?topic=11761.msg85946#msg85946 to get 6+ cards running under windows 7. I'll stick with 3.4 for now but anyone else having similar issues?