There is no way to accurately gauge the potency of any given batch. There is no recommended dosage for street drugs since what you have is inevitably going to be different than what someone else has. The rule of thumb is to dose very low and slowly titrate your dose upward.
Assume there is fentanyl in the stuff you have. The best way to dose is to use volumetric dosing so you can be sure there isn't a hotspot in the powder from poor cutting methods.
Don't underestimate the strength of fentanyl/heroin/china white, you can still very easily OD with a tolerance like yours. I hope you change your mind about using this stuff but if not, use volumetric dosing to be as safe as possible.
