Tyvm FIY, I have 50 rigs 3x290, my total hashrate ~500MH, I'm using d=0.01 now, if I only mine x11 and x13 then do you have any suggest which diff should I set?
You should adjust difficulty for each separate miner (rig), that said, if you have multiple rigs, each rig with 3x R9 290 that makes about 10Mhs for X11 per rig, and if you look at
this table this results in a suggested diff d=0.08. Even if you're mining with several rigs at the same BTC address, you should set diff for each separate rig, not for the combined hashing power of all rigs.