If you want to be scientific about it you need to consider lots of different things. There is what's considered a healthy range seen in non-diabetics. There is a range outside which you start seeing clear diabetic symptoms. There is a range that balances how easy it is to stay within that range and how sustainable it will be for you versus your individual risk factors (how your body works, what meds you are on, etc). I like a challenge and I've picked mine to roughly match non-diabetic range (4-7mmol/l). I tend to be a bit of all or nothing person, so that is right for me. I also had a conversation with my GP to get support around managing my meds alongside my quite intensive dietary interventions, primarily to reduce meds that could cause me hypos, but also review all other medication and agree a path forward with some success metrics for next lot of blood tests. Will this be the right thing for others? Might or might not be.