Medusa 3400 (3400 kv, 10 T pinion)
vs.
Neu 1107/2Y (3400 kv, 10 T pinion)

Both motors were installed in the middle T-rex below.  The heli was identical in both cases except for the motor swap.

On Day 1 the Medusa 3400 motor was flown as the Jazz governor was changed to different values. 75% seemed pretty good with a headspeed of just over 3100. It flew really smooth with the relatively weighty Mavrikk carbon fiber blades. Climbout was very good and it has plenty of power for most anything. The voltage, current and power graph is shown below.

Hover current was in the 10 to 11 amp range and full climbs peaked at just under 27 amps. The batteries were only warm after the flight, the motor was pretty hot and should probably have a heat sink installed, especially for summer flights.

On Day 2 the Neu 1107/2Y motor was installed; all other equipment was left unchanged. Again, the Jazz governor was varied and the data was plotted from 80 to 95%. Oddly, the headspeed didn't change all that much and maxed out at about 3060. The batteries and the motor were only warm after the flight, both were in the 90's (F).

Hover current was around 10 or 11 amps, about the same as the Medusa 3400 motor. Max current during full collective climbs was about 25 or 26 amps, almost the same as the Medusa motor, perhaps one amp or so less.

Summary

The T-rex flew very nearly the same with both motors. I would be happy with the performance of either motor, they both have LOTS of power and the flights were very smooth with the Mavrikk carbon fiber blades. I expected the Neu motor to turn up a few more RPM's, I stopped pushing the governor any higher when the Medusa motor was spinning the head just north of 3100 RPM;s. The Medusa motor is a bit lighter (without a heatsink) than the Neu motor and is less expensive.

The bird flew essentially the same with both motors and there was almost no difference. However, if I was forced to choose (almost a guess actually), I'd have to give the very slight edge to the Medusa 3400 motor; possibly due to the tiny bit of extra headspeed with the Medusa. Again, I thought the difference in the 'feel' of the heli was essentially non-existent. If fact if someone swapped out the motors and didn't tell me, I'm sure I would not know the difference.

Some related info:

(I also have a Medusa 2800 motor on 4 Cells in a stock gray plastic framed T-rex with the DIY ccpm mod and set up with similar equipment . This bird has the lightweight newer gray Align wooden blades and it rocks. It's noticeably friskier then either of the two T-rex's discussed above. It has a slightly lighter overall weight and lighter blades. This T-rex with the Medusa 2800 hovers around 11 amps and current peaks are around 20 or 21 amps.  It would be interesting to try the Mavrikk blades on the Medusa 2800 bird so see how it compares to the two above. I'll try that a little later. :-)   I'll also try the Neu motor above on the newer TP Pro Lite 21000 4 Cell pack to see if there's any difference; although it doesn't seem to be straining the 2000 Pro Lites, but in the interest of science it needs to be tested. :-)

All these T-rex's are a blast to fly and I would quickly recommend any of them. Half the fun is trying new things. Next I'll try some very lightweight carbon fiber blades to see how it affects the handling.