Try ...
"roundsievepercentage" : 20,
"sievepercentage" : 8,
"sievesize" : 100000,
Thanks for the tip - I'm now getting 11k pps - I'm getting about 20 cpm now but it will randomly drop down to 10 cpm and then jump back up
23:32:42

{
"blocks" : 83418,
"chainspermin" : 21,
"currentblocksize" : 1000,
"currentblocktx" : 0,
"difficulty" : 9.26809406,
"errors" : "",
"generate" : true,
"genproclimit" : -1,
"roundsievepercentage" : 20,
"primespersec" : 11280,
"pooledtx" : 0,
"sievepercentage" : 8,
"sievesize" : 100000,
"testnet" : false
}