Don't forget to allow for hop utilisation--this decreases as wort SG increases, quite dramatically once you get past OG 1080. The Russian Imperial Stout that is currently ageing in a cornie I reworked the hop additions allowing for a SG 1130 wort and ended up increasing the bittering addition from the 179g in the CAMRA book to 350g!
Haveing used fresh, REAL amber malt I now understand the description "Stunningly dry, bitter black chocolate on the tongue . . ."
If you use grumpys calculator, you should look at the table for utilisation efficiency in Palmer's book. Grumpys' default setting is for a low gravity boil and presumes quite high extraction - in the 20s% I think. Better to enter your own eg for 90 minute boil at 1.080 you will get about 17% extraction.
Sorry fellas, i should add that i am doing an extract + grains brew. So i guess all of the bitterness hops will come from the can, so i guess that any hops i boil after i have steeped will just be for taste not bitterness?