Lightbringer, like I said I have that motor in my Hobbyking Reaktor. According to my records, I have 97 flights with that motor in the plane (I actually have 123 flights on the plane, but that motor was the third motor I tried in it, and the best one). The ESC I have in it is an 18-amp Plush.

I am using a GWS 8x4DD prop with it, and my records also indicate that the ground wattmeter test I did on it with that prop and motor showed 12.3 amps, 140 watts, voltage drop from full charge (12.6V) to 11.4 V. That was using a Zippy compact 850 mAh 3S, 35C.

Since you indicated interest in using a GWS slowfly 8x4.3 prop, I checked my records and yes, I do have a couple of those in my prop collection (I've got probably over 100 different sizes/kinds of props that I've collected over the years in there...). I fished out the prop from the bin, then ran the motor on the Reaktor up with that prop, together with one of my Zippy compact 1000 mAh 35C LiPos. It pulled almost exactly the same amps and watts as the 8x4DD.

Usually motor specs include a suggested max amps. In this case though, they just give watts -- 160W. Simple math shows that with the expected voltage under load of a 3S LiPo of 11.1 volts: 160 divided by 11.1 equals about 14.4 amps. So an 18-amp ESC would do the job with room to spare (as it has for me, for well over a year). A 20A would be fine too, if you want to go with that UBEC (hopefully switchmode BEC) ESC.