This planet is the fifth planet from the star, at a distance of about 0.25 AU (compared to 0.39 AU for Mercury) with negligible eccentricity.
HD 40307 f's minimum mass is 5.2 that of Earth, and dynamical models suggest it cannot be much more (and so is measured close to edge-on). Planets like this in that system have been presumed "super-Earth".
Even though HD 40307 f is closer to the star than Mercury is to the Sun, it gets (slightly) less insolation than Mercury gets because the parent star is dimmer than our home star. It still gets more heat than Venus gets (like Gliese 581 c), and it has more gravitational potential than Venus has. HD 40307 f is more likely a super-Venus than a "super-Earth".
Moreover, planets b, c, and d are presumed to have migrated in from outer orbits; and planet b is predicted a sub-Neptune.