Likewise, please do not take this the wrong way, it is for constructive discussion. I have been running the GTB ESC with the fan on my Xray T2 eversince I got it and it definitely does not have any thermal issues irregardless of chassis location. Rather it is the Velociti 5.5R motor that is getting the thermal issues even when using the recommended FDR or higher.
On the other hand, I have used the Nosram Storm 3-Star motor (which I reckon is similar to LRP Vector) with the GTB and it is certainly able to withstand a much higher temperature. Unfortunately for 2 friends of mine at our club, the temperature apparently got too high and their 3-Star rotor magnet cracked during the last minute of 7mins heats. They broke 3 motors in between them.
Also for this 3-Star motor that I got, one of the three 1.5mm screws securing the endbell was bent out of shape within when I disassembled it for my first maintenance. I am not sure if this was due to the result of use, or a factory assembly problem. Anyway, the Velociti is certainly more robust in design, although heavier.
I would like to try the LRP Sphere Competition when budget allows, soon I hope.