Here are the results all together for all motors tested in the video. The Rated number from the spec sheet will be on the left, followed by the number i have measured on the right.

GCool RC 3650 4300KV@£15.99
Rated Measured Difference
4300KV 4275KV -25KV
2.7A 7.4A 4.7A

GCool RC 3650 5200KV@£18.79
5200KV 5090KV -110KV
3.7A 7.1A 3.4A

Surpass Hobby Classic 5900KV@£19.43
5900KV 5812KV -88KV
5.2A 4.7A -0.5A

Surpass Hobby KK series 6900KV@£19.68
6900KV 6858KV -42KV
5.4A 4.8A -0.6A

None of these motors managed to hit or exceed their rated spec in terms of real KV. However they were all close enough to be considered ok, the analyser state and accuracy of +/- 3% so i would regard anything within 3% to be ok.

Clearly the two surpass motors were much better when it came to their amperage. They came in under spec which is good because the lower amperage shows they are more efficient and produce less heat.

On the GCool side things were not so cool. I felt the 4300KV is much louder and nowhere near as smooth as it should be, while the 5200KV version had a more reasonable sound level, it still fell short of the higher KV surpass motors. They both used much high current than the spec sheet says and the 5200KV motor was already warm after just this short test. It is quite funny considering it was the only one that came with a "warning hot" label :D.

Even though these motors tested were not directly comparable If you are looking at these motors on ebay, I would choose the surpass motors over the GCool motors. Especially if the are the same price.
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https://www.youtube.com/watch?v=6ca2n28xF-w