1kg of frame weight? - plastic only? - without motor and battery?
With this span if you go beyond 900grams the flight will be very very difficult.
I've been flying nitro aircombat models (http://www.aircombat.pl/ACES) - your model also fits in 1:12 scale - so these are same animals.
But our models were 0.9 - 1.1 kg ready to fly with fuel. And they were very difficult to hand launch.
The optimum weight for this model to fly resonably is 1 kg max... - the lower the better.