Just going to throw this in a well.
I agree perceived is hard to really calculate from person to person. It is simply that the more non-fermentable dextrines that are in your wort, the perceived bitterness will be lower. 80IBUs suddenly tastes like 20-30IBUs. Same goes for the other side, if the beer is dry and hoppy. 80IBUs may seem like 110IBUs.
This happens a lot in BJCP competitions. While the minimum IBUs for a IIPA is 60IBUs, no one is going to get a good score with that low of IBUs on a IIPA. This is simply because the IBUs are not pronounced enough for the other guidelines in the IIPA category.
So now that that is out of the way, let me talk about your actual question.
If I take 45lbs of grain: 40lbs of 2 row, 2lbs carapils, 3lbs belgian candied sugar for a 5 gallon, mash at 144^dF for 1.5 hours. Boil 90min and add 2oz Cascade at 90min. Ferment slightly colder than suggested on a Ultra High Gravity yeast. Now I have a 17% barley wine with maybe 20IBUs that is going to be bone dry.
Now I take the same beer: 45lbs of grain: 40lbs of 2 row, 2lbs carapils, 3lbs belgian candied sugar for a 5 gallon, mash at 154^dF for 1.5 hours. Boil 90min and add 2oz Cascade at 90min. Ferment at suggested temp on a Ultra High Gravity yeast. Now I have a 17% barley wine with maybe 20IBUs that is going to be a malt bomb.
So you need to know a few things to figure out which side of malt or hop bomb you are going to get. Of course, that second beer with 20IBUs is not even going to taste like hops are in it and the first will have a little more of the bitterness.
Hope that helps!