I stopped sub-q long ago. I go IM for GH and insulin. The only thing you have to do is figure out how much faster insulin hits you when you go IM. It hits me about 15 minutes faster...once you do that you're golden.
I do IM for my growth because I would never put a cc of water in my fat at once. Peps are only .20 ml but anecdotally I've found I feel ghrp hit me harder IM. I use a 29 slin pin in delts or upper pec. Occasionally lat if I haven't pumped them full of oils already.