75mg/ml fina that is properly filtered (in other words, no gunk binders) will definitely go through 25 and 27 and even 29 G needles, but i would not recommend using 29.... it definitely requires patience and a strong hand (you are working it out, right?) in order to push such a viscous fluid through it, but when you consider that both 300mg and 400mg nandrolones, which are almost as thick as molasses can go through these needles (with alot of suffering, but they do), sesame seed oil and similarly based substances are a bit of a challenge, but totally doable......
in other words, yes, you can use even a 29 G needle, but if you want to keep your sanity (and you feel your forearms are big and buff enough), stick with 25g needles