In general, Power Diss. can be impacted by Gate-Source Voltage, have you noted 6679Z and 6679, The value of "Z" is -25/+20V, but the value of "6679" and "AZ" is -25/+25V, It's hard to check out if you only review thru. the picture, because actually, Fairchild has many many suppliers and that will be different if the packing location is different;
One more, you'd better to check the requirement of your project and according it to select AZ or Z or 6679 only.