Well Joe, while we're all trying to rain on your parade, just a couple more things to think about.

If you go the bigger rotor, your ralleys may not fit. I'm assuming you have 15" ones. With a 12" rotor, and the caliper hanging above it, it probably won't clear anything smaller than 16" rim. Check that first. Positive offset wheels are okay to a point. If you go with a positive offset wheel, AND spacers, then you compound the load problem. Not only will you have the spring issue that Don mentioned, you'll also increase the leverage on the front wheel bearings.

BTW, it wasn't clear to me whether you were trying to get 3" wider overall or per side.