I remember the mouse being naturally quite sensitive in SS, I don't think it helped by quite a low FOV. The slider that controls sens is also very strange, I don't think it is proportional/linear. But I'd recommend you try lowering the setting.
Also I may be confusing it with another game, but I seem to remember a "reduce mouse lag" or "disable mouse smoothing" setting or similar. Try disabling that as you may be one of the players who prefer a slightly less responsive mouse than feels smoother.