As far as I'm aware (and based on the study with this doi: 10.1007%2Fs12630-019-01294-y) carfent is estimated to be 20-100 times as potent as fentanyl. If this is true, the same way that fent was used to cut H to make it more potent yet also more dangerous, carfent is in the same position relative to fent.
There simply haven't been proper human studies to provide an accurate value for potency. What I HAVE noted is that the more potent an opioid is, the more it's potency differs between people. I wonder if that's why super-potent opioids aren't more common? It's simply impossible to provide an appropriate dose - one person feels little, another turns blue.
I've noted that it seems more common among the non-rigid classes which makes me wonder if it's the docking that results in such differing potencies. About the only thing I trust is the RELATIVE potencies given within a single paper as they will use the same protocols for all homologues.
I've posted a link to a paper covering the relative activity of oxymorphone, metopon, 14-methoxymetopon and 14-methoxy-N-phenylethylmetopon. The last of these is around x500 M and by all accounts, the few papers that cover it all seem to conclude more or less the same potency.
I'm in no way suggesting that N-PE-14-OMO is an appropriate or desirable product, but it appears to display subjective effects similar to oxymorphone. Now, I've never sampled oxymorphone but on Opiophine, it was voted the most euphoric opioid among a group of people who had sampled hundreds of compounds.
To my mind, this would obviously not be a compound to be sold as a powder. I suppose windowpanes would be the cheapest way to ensure reliable doses but if one were going 'premium', I imagine small white pills with, I dunno, 0.2mg in each?
OT many years ago I met a couple of Dutch guys who had worked out how to produce a bicolored tablet. One face one colour, the other another. They kept exactly how they did it a secret but it was intended to be a 'seal of quality' for the high quality MDMA actually used by the Dutch.