Yes generally with a large beer you have to boil longer since you need to sparge with more water to get the same efficiency. On the other hand you can just plan for a lower efficiency and put in more grain, I generally think another pound or two of grain is worth the extra hour and use of propane to boil off more.
"People should not be afraid of their governments. Governments should be afraid of their people." - V
Secondary: Shady Lord RIS, Water to Barleywine, Pumpkin wine, burnt mead
Kegged: Crappy infected mild
Bottles: Apfelwein, 999 Barleywine, Oatmeal Stout, Robust Porter, Robust smoked porter, Simcoe Smash