It's really hard to calculate ice beers from what I read. It all depends on what the alcohol is to begin with, and how much water you take out. I think with a typical eisbock you should be removing around 1/3 of the water in the beer. This would make me think that the alcohol should go up by 1/3, but I'm not sure. It's late, and my brain doesn't want to function correctly.
There's no need to bring your freezer to -10F. Beer will freeze at around 28F (depending on abv) in around an hour.