I can't say, since I have never IMed this. I have IMed MXE a few times and it was definitely stronger than oral, but not sure if it was as strong as rectal... rectal is VERY strong with MXE, I've found. I don't know if the same holds true for 3-MeO-PCE, as I've never tried that one rectally, either.
In general, my understanding is that IM and rectal administration are very similar in terms of kinetics and such. I would proceed with the expectation that it will be about similar, if you decide to do it. The safest approach would be to assume IM is stronger, but if you don't get many opportunities to yourself, knowing you're experienced and that 25mg rectal was fine for you, it would probably be okay to do that dose via IM.
However, if it were me, I'd just plug it. IMing is risky even if you're careful. The last time I IMed something (MXE), I had a sore spot that even got warm for a day, I was watching it like a hawk, but it went away after a couple of days and got steadily better after it got warm, and didn't spread. But it scared me. You definitely don't want an abscess. Rectal is much safer.