For whirlpool/steep/hopstand/post-flameout additions, I've been using the free BrewCipher spreadsheet for IBU estimations. Having just did a beer similar to Levitation with nothing but flameout hops and a 30 minute no cooling steep, I found the estimate IBU to be pretty close to how I perceive the actual bitterness.
Another similar exercise is to compare Mike Tonsmeire's Modern Times recipe of Fortunate Islands to that on his home system. His homebrew versions have more finishing hops than the commercial version, simply due to his lower hop utilization (bitterness, flavor and aroma).http://www.themadfermentationist.com/2014/03/fortunate-islands-homebrewed-yeast.html
The one thing I'm discovering about this beer (heavy on crystal malt) is that the character of the beer changes quite rapidly going back and forth between hops and malt, and not always in a good way.