As I said earlier, some of the steepest hills I've encountered were in "mostly flat" places. Steep areas generally have paths/roads/tracks that take the line of least resistance rather than go straight up and over.

How many bridges, on ramps, underpasses and out of town excursions, will you want the bike for? If it's more than cruising around the centre of town then I'd be inclined to go for gears over SS.