Hi,
I found, for 2.5 D of flying, even honestly rated 20 or 25 C packs are good. My calculation goes 300-500 W per kg, so with a 20 C pack 5 Ah x 22.2 V = 2,200 W / 500 W would be good for a 4.4 kg model
But on the other hand (for hard 3D/competition flying), such packs will probably not have the same punch and will probably not last as long as higher rated packs, both because the voltage curve is lower, the voltage will drop more in very high load situations, and they probably get hotter.
Kind regards
Eddi
Born to fly ...
forced to work.