Voltmod... hmm cooling sufficient? Stable? 15-20% is huge... and any delays and problems at current increasing difficulty... we get lucky if we do even a small profit.
Agree if you know what you are doing
For starters i will do voltmod on 15 PCB and I will test it a few hours. If there are no problems, the voltmod will continue.
According to the russian consumers, voltmod strongly increases power consumption of devices. We have a triple device and there will be a few in the same room. Therefore, the temperature can limit the overclocking. But the effort is worthwhile.
Don't push them too hard and stay within a safe margin. Assuming you won't add additional cooling it sounds rather risky and a 20% performance increase is not worth it if it means frying half our PCBs within the first month.