I have been quite satisfied at 3mm, just a condensation leak occasionally, as you point out. I simply want to go a bit beyond to see what will occur for my own curiosities sake. I have been vaping 5 Protanks and 4 eVods with this 3mm, 4 wrap method and I am very satisfied with the result. The low ohms gives more, warmer vapor to add to an all around better vaping experience.
The extreme fluctuation of heat from 60 degrees am to 95 degrees pm in Florida tends to cause a sweating of the coil that produces a small amount of condensation to appear at the bottom of the atomizer, old wick style or new. I am afraid 8mm would not prevent it. Anytime you have a soaked wick suspended above an open hole, there will be some leakage... there is no remedy for it and it is not that objectionable.
I vape from 100% PG to 100% VG and anywhere in between, I think you will do well with 3mm, as many others will attest to.
Also, if you have restricted the airflow of the eVod or Protank you may want to open that up after rewicking, the new wicking restricts the airflow even more so it may cause dripping because the airflow is too choked off.