These are my settings...

velocitycoinminer -o stratum+tcp://stratum.cipherpool.com:8843 -u user.worker -p passw --scrypt --Nfmin 4 --Nfmax 30 --StartT 1387769316 -I 16 -w 512 -g 2 --auto-fan --thread-concurrency 8192 --scan-time 5 --lookup-gap 2

i get 1% HW errors but this is the max adjusted speed for me.