The most efficient public miner is 1gh cpuminer-cryptonite.
My hashrates were for comparison within the range of the same software.

I know it may be already obsolete if private miners are in the game.

The hashrate increased rapidly in last hours.

Some statistics:
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"blocks" : 12533,
"networkhashps" : 1863253147,
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"blocks" : 13341,
"networkhashps" : 2534603317,
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"blocks" : 15322,
"networkhashps" : 4792662628,
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just four hours later:
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"blocks" : 15556,
"networkhashps" : 6284523620,
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