Well, I'm afraid that it's a trade off. With Ketamine I won't go past 100mg/ml and it's about 50% heavier than Methamphetamine. I would prefer injecting less than 3ml, but it just isn't very sustainable that way. I would suggest you use 70mg Methamphetamine HCl for each cc of bacteriostatic water. No need for any benzyl alcohol since it's in there.
The pH of the liquid should ideally also kept close to physiological pH, but with buffered solution you would be best off to stay even much lower than that concentration. With a strong acid and a weak base methamphetamine in water should be slightly acidic, right? The healthiest is definitely a slow infusion of a relatively large amount of liquid, ideally even with a buffer to keep the pH neutral. I am not sure if the drop would be significant enough for damaging tissue, probably not. Maybe you could tell us.
Another factor to consider is damage specific to the respective chemical, e.g. ketamine is a vasoconstrictor and will contribute to tissue becoming necrotic, only when there's enough ketamine and especially when it ends up outside of the vessels. I don't know about meth, probably not too healthy either. The really nasty ones are some cytostatics which will basically eat away your arm.
