Ive been mixing oils with oils and with waters i dont think it matters, they are all going in anyway. When doing Prop i never experienced pain but also had it watered down (meaning cocktailed so i wouldnt feel pain anyway). Also when doing the injection rubber top, vial or anything, the need gets dulled if anything vials are much worse on the sharp tips of a syringe needle. But reccomend use a 22G to withdrawl(load) then switch needles to 25g to inject.
This is the norm i hope this helps people.