Unboiled wort what what? Don't add unboiled wort to your fermentor. Grain is silly with lactobacillus.
In any case, the various hop formulas scale linearly...so if you calculate 70 IBU in 5 gallons, you'd get 35 IBUs if you then diluted those 5 gallons to 10 gallons.
75 IBUs in 7 gallons should be about 48 IBUs in 11. If you want 70 IBUs in your full 11 gallons, you should shoot for about 110 IBUs in your 7 gallon boil.