Some companys' manuals present quick turnaround limit weights for both flap 30 and 40. Those who operate from high altitude and high temperature airports, a flaps 40 landing may not be an option because of the approach climb limit weight.
Generally, approach climb performance is not a factor at low elevation airports. If the operator ala FR is looking for a quick turn time of 25 minutes then flaps 40 may be the only option, unless the crew wants to fly with the gear extended after takeoff for a period of time.
Get your hands on your company's actual Planning and Performance Manual (P&P). The P&P contains data for both flaps 30 and 40 quick turn limit weights, while the FCOM PI/PD sections contain excerpts from the actual P&P. You will see that a flaps 30 landing will result in a lower quick turn limit weight due to the higher break energy limit required to stop the aircraft.