Well, as it turns out I made a rookie mistake. It appears that the RPM that I would like to use on the 12x6 and 11x5.5 are higher than what people normally use, but more importantly, for the 11x5.5, using the 4S pack with a 870Kv motor is not a good idea if you are trying to reach over 10000 RPM. In essence, the max RPM is limited by the voltage (Kv * Volts) and ideally you want to run at about 80% of your no load RPM for a given voltage. In essence, for the 11x5.5, I was pushing the motor pretty close to the limit of what it can do on 4S. Changed the pack to 5S and the current dropped to 25 amps or so rather than the nearly 40 amp needed when using 4S.
In the end it appears that the Hacker motor is about 10% more efficient than the E-flite which is something that I will keep in mind for the future. Right now, the Eflite will go into the model I am trying to finish as it was build around it. The thing that was interesting is that the Hacker was meant for a largish parkflier and in principle it should not have the power of the Eflite. Go figure.
Teo