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 . . ."