You'll want to use the highest temperature the beer reached after CO2 production stopped. If there was fermentation going on at 40°, and it never got any warmer afterwards, then use 40°. If you had it warmer for fermenting the fruit, and then cold crashed it, use the warmer temp. As mentioned, the reason the temperature is needed is because how much residual CO2 stays in solution depends on temperature. Warming the beer up will cause the CO2 to come out of solution, but cooling it down doesn't cause the beer to absorb or create any additional CO2.