Meldex (and Soay),
airspeed calibration. Don't compare apples with oranges. Figure out the stalling speed in CAS, then compare.
If you read section 5 close enough you will notice a different airspeed calibration between those two models.
Especially in the low speed.
Actual stalling speeds in CAS:
DA40D: 54kt (1150kg)
DA40NG: 58kt (1280kg)
DA40NG: 55kt (1150kg)
So basically, its a wash.