experimental report
I have tried this comparison experimentally. I had a decent bulk amount of one batch of light tan powder. I tried these methods a week apart without using in between.
Plugged
I measured out 30mg of powder, dissolved in water, then plugged (after a BM, and layed there for 15 minutes). About an hour later, not feeling much, so I plugged another 15mg. Half hour later, not feeling much, plugged another 20mg. Feeling barely high, but not satisfactory. So this was 65mg in the course of 2 hours.
Snorted
I measured out 30mg. After rinsing out with saline spray, snorted softly as to avoid drip as much as possible. After about 5 minutes I sprayed with water to aid absorption. Hour later, not feeling much, snorted another 15mg. Starting to feel itchy, good sign, but not blasted yet. Half hour later, snorted another 20mg. Now I feel very itchy, tingly, and satisfactorily high. This is 65mg over the course of 2 hours.
Conclusion
I am recalling this experiment from memory about 3 weeks ago, so the doses for either method (or both) could be off, but I doubt they are appreciably off. Also, the fact that these doses are spread out over 2 hours may distort accuracy a little, due to differences in absorption time and metabolism between rectal and nasal.
However, as it stands my intuition tells me that snorting is more efficacious than plugging. I was getting noticeably higher every time I snorted additional doses than I did with plugging additional doses that were very similar in weight. The progression was obvious. Also, I think it is important to note that when plugging heroin, the high was much more morphine-like. There was the classic histamine head-pressure that I get with morphine, and the same heaviness as well. This did not occur when snorting, which actually resembles oxymorphone in quality more than it does morphine. This morphine-resemblance when plugging makes me think that a substantial portion of the dose is NOT avoiding first-pass metabolism, as it does when snorting. So, I know this experiment has weaknesses, but it's certainly better than most reports here since the doses were measured out.