I wouldn't be surprised if the A11 Fusion chip has a much superior implementation of the big.little architecture than the one ARM has. Actually, its quite likely as the controller is sophisticated enough to use little cores to significantly boost performance in multi-threaded code.
I do not think there is evidence for this. In contrast i can get significant speed-ups when using all 8 cores instead of the 4 large ones when running multi-threaded code on Snapdragon 835 - which does not even feature a DynamIQ implementation.