setx GPU_USE_SYNC_OBJECTS 1
velocitycoinminer.exe --scrypt -o stratum+tcp://velocitycoin.miners-point.com:3352 -u myusername -p mypassword --scrypt --Nfmin 4 --Nfmax 30 --StartT 1387769316 -I 16 --auto-fan --gpu-engine 965 --gpu-memclock 1250 --thread-concurrency 28632 --scan-time 1 --queue 0 --worksize 512 --gpu-powertune 20 --lookup-gap 2 --scrypt
I use a variety of settings for r290's. Sometimes a good old fashion reboot is in order when my hashrates drop and play up.