Insanely fast renders ? Your facts are wrong
Usually CUDA will give a speed boost of 2-10X compared to the CPU , not a small boost by any means but nowhere near to insanely fast. The speed boost of course will depend on your GPU specs.
Generally speaking if you do heavy renders a render farm is mandatory. You can rent one online and they tend to support all major 3d apps, including Blender. Blender also has some free render farms online. A big enough render farm can give you insanely fast speed depending on its size but since they tend to cost tens of thousands of dollars or euros its much better to rent them.