The G-force that the driver's body is subjected to while braking is magnified by the grip and the aerodynamic load. Braking performance being equal, indeed greater load force and grip force contribute to increasing the G-force that the driver experiences. This is why the braking sections with greater G-force are found mainly on the inside of circuits with medium-high aerodynamic load.
On the other hand, on tracks where the drivers reach extremely high speeds, in spite of low aerodynamic load, the G-force is high due to the brutality of some of the braking sections and the intense reduction in speed. Taking into account the entire 2016 Championship season, there are about thirty turns marked by a negative-G (deceleration) not less than 5, and about fifty that start at 4-G. On the contrary, there are only twelve turns in which the drivers are subjected to less than 1.5-Gs.
The most difficult by far is expected to be the Prima Variante at Monza, or rather the first chicane after the Italian finish line where the drivers arrive at about 350 km/h, followed by a 6-G deceleration. Second to this, in view of data Brembo has available, ought to be turn 12 at the Circuit of The Americas in Austin. Trailing closely behind, with fairly similar numbers, ought to be the Louis Chiron turn (turn 13) in Montreal, the chicane at Eau Rouge in Spa, the Elf turn (turn 1) in Barcelona, and once again Monza with the Variante Ascari.