IBU in recipe formulating question. Help please?

I'm working on formulating an Imperial IPA recipe.

I'm pretty set on the grain bill. It's a 5 gallon batch all grain.

10 lbs 2 row
3 lbs Maris Otter
1/2 lb Amber Malt
1/2 lb Crystal 60
1 lb sugar during the boil

Est. O.G. - 1.083

I'm going to be using Warrior, Horizon, and Simcoe hops.

I plan on FWH with some Horizon, and using Warrior for bittering @ 60. Then loading up Simcoe and Horizon on the back end.

Now, If I want most of my hop additions to come in the last 10-15 minutes of the boil to get huge flavor and aroma, how much IBU contribution would I need in the early additions for bittering to offset the higher O.G.?

Using BeerSmith, using 1/2 oz Horizon FWH, and 1 oz Warrior @ 60 gives an IBU contribution of about 56 IBU's. Is that enough if my total IBU for the beer will be around 100?

Also, for what it's worth, I will be using either White Labs WLP001 or WLP060, both of which attenuate pretty high and accentuate hop character. With that, should I even worry THAT much seeing that there won't be as much residual sweetness left behind?

Any input or comments are welcome. Thanks!

You could go light on your FWH and 60 charges, and dial up your late additions if you want "huge flavor and aroma."

If you're shooting for 100 IBU, you could consider a hop schedule like this (choose which varieties at which times you like):

30 IBU FWH
40 IBU 60 min
17 IBU 15 min
8 IBU 10 min
5 IBU 5 min

That way you'll get your desired IBU balance, but boost the wort with some strong aroma and flavor additions. Perhaps add in some flameout hops and/or dry hops too.

TB