I am not opposed to using 4" (unless there is a reason I should be), I just figured I would use 3" because it seems much more readily available. Most of the sites I am considering shopping from only seem to have 3" and 11", that's really all that had guided my decision. I know 11" is too much though.

I usually keep the temps in my apartment fairly low in the summer, so maybe I should go with the two strips. I don't want to overdo it though, there's always the horror stories of thermostats sticking wide open and frying the snakes.