Ah... That sounds excellent! I actually remember now where I was thinking of the bottlenecking conundrum—Thunderbolt 3 and dual-core Windows tablets. As I recall vaguely on the Eve Community forums from a year or so ago, someone had posted test results of scaling with either an Asus Transformer 3 Pro or the Eve V. They had found that the GTX 1060 was the practical limit due to CPU bottlenecking.
With Thunderbolt, you have the additional hurdle that you are not using the PCIe lanes from the CPU, but those from the chipset. For both Intel and recent AMD (post Ryzen) platforms that means effectively the GPU needs to share a PCIe 3.0 link with all the other chipset-connected components, and on Ryzen all the chipset lanes are PCIe
2.0 only. The Udoo is using the V1000 embedded SoC, so there is no chipset. Instead, those 4x 3.0 lanes come directly from the CPU.
PCIe bottlenecks in GPU performance mainly scale with framerate rather than GPU performance (i.e. the more frames you render per second, the more 'chunks' of data need to pass from the CPU to the GPU). As the V1000 CPU is pretty slow, you're unlikely to be reaching a high enough framerate in the first place for PCIe link bandwidth to be the main limit of performance.
