I've actually read a lot of arguments that boil gravity doesn't affect hop utilization as much as people once thought. And judging from my own experience I would agree, especially with gravity gained from extract additions. That being said, whenever I use extract I still add it at flameout, but just because it has already been boiled once in the drying process and boiling again only leads to darkening and caramelization. I just don't trust the extra IBUs my software says I gain from checking the "late addition" box. Also, not doing a full boil is going to weaken the hop presence in the final beer, so I think 1 oz would probably work well and you might even want to think about more for the bittering addition.
I actually just brewed a winter warmer last weekend, though my OG was lower than yours (1.065). I used 0.75 lbs crystal 40L and 0.75 lbs crystal 120L. I can't really say if it turned out well though, because it's only been in the fermentor for a few days now. But I think that is a pretty good amount based on looking at a bunch of other recipes. I might even go higher for your recipe because your OG is going to be a lot higher. Here's my recipe, just to give you an idea:
Brew Method: All Grain
Style Name: Holiday/Winter Special Spiced Beer
Boil Time: 60 min
Batch Size: 5.5 gallons
Boil Size: 7.25 gallons
Efficiency: 70%
STATS:
Original Gravity: 1.065
Final Gravity: 1.016
ABV (standard): 6.4%
IBU (tinseth): 44.28
SRM (morey): 25.71
FERMENTABLES:
7 lb - Maris Otter Pale (50.9%)
4 lb - Munich (29.1%)
0.75 lb - Caramel / Crystal 40L (5.5%)
0.75 lb - Caramel / Crystal 120L (5.5%)
0.5 lb - Chocolate (3.6%)
0.75 lb - Smoked Malt (5.5%)
HOPS:
0.5 oz - Simcoe (AA 14.1), Type: Leaf/Whole, Use: First Wort
0.5 oz - Magnum (AA 13.5) for 60 min, Type: Pellet, Use: Boil
1 oz - East Kent Goldings (AA 5.8) for 10 min, Type: Pellet, Use: Boil
MASH STEPS:
1) Temperature, Temp: 154 F, Time: 60 min, Amount: 18 qt, Strike temp = 167
2) Infusion, Temp: 170 F, Time: 10 min, Amount: 9 qt, Mashout
3) Sparge, Temp: 185 F, Amount: 10 qt, Batch Sparge
OTHER INGREDIENTS:
1 tbsp - Crushed Allspice Berries, Time: 5 min Boil
0.5 oz - Sliced Ginger Root, Time: 5 min Boil
2 each - Cinnamon sticks, Time: 5 min Boil
0.5 tsp - Irish Moss, Time: 15 min, Type: Fining, Use: Boil
YEAST:
Fermentis / Safale - Safale - English Ale Yeast S-04
Hope this helps.