Efudd’s modified firmware for the Bitmain AntMiner Z series ASIC miners now supports the Bitmain AntMiner Z11 with its latest update to version 2.3, AntMiner Z9 is supported by version 2.2 and for the AntMiner Z9-Mini you need to use the version 2.1d. The modified firmware allows for more advanced overclock including frequency and voltage tuning with voltage controls per hashboard option available. With the modified firmware it is easier to achieve higher performance than with the stock firmware that has limited OC capabilities by Bitmain. According to the developer of the modified firmware 150+ KSol/s (up from the stock 135 KSol/s) should be doable with minimal tuning and further increase to 170-180 KSol/s might be achievable with more power, careful tuning, good cooling and some luck.
Do note that the modified firmware comes with a built-in 3% developer fee, so the miner will be mining for the developer 10 minutes out of every 330 minutes it is operating.