and it was not only GB cup, we had also such famose models like loopings flying B17 

No, I never saw problem with weight of the foam. We use even parts with printed UV colors, and it is even heavier. But for info, that model which I built for Paul and John which is without colors, weights 206 grams, tip weight is 12g, battery weights 48g, motor 32g, esc spin 11 15g, prop 7g, active timer 4g, and may be some parts like fixing for battery and "X" for fixing motor can be 3g

... so my empty frame without colors like your now could be somewhere at 85g

my yellow model is 10g heavier (plus color and plus some repairs) and I cannot tell any difference, but you will see

however Tania has much lighter model (even with colors) which is attached on picture, I tried it and it flights very nice, but it is without active motor controll and that makes large difference  in weight, but it does not keep speed well, so I would definitelly choose my heavier version

it is difficult to tell you, simply try it and you will see the result, it will certainly help, but I affraid of stifftness.

I do not know that motor, but that type which we use is 60W motor with kv=1400 and IR=150mohm

9"prop will be too little I think