For 290 miners with 4gb of ram:
--intensity 18 --thread-concurrency 42000 --gpu-threads 1 --lookup-gap 3 --worksize 64
This will net you 135 khash. Tomorrow I will try gap 4 but I really doubt it will lead anywhere. Thank you Puycheval for worksize modification.
With 4/6GB of ram 290 RIGS must be --lookup-gap 3, it works but only ~140khs vs 8GB ~180khs
Looks 8GB is necessary to 290 rigs
--lookup-gap 4 is lower hashrate ~115khs
Good job!:)