Wi-Fi. If by 'another Wi-Fi' you mean another fullnetwork, speed testing on my home network brings expected results with both the N4 and N10 (i.e. my ISP's normal bandwidth). And, no, nothing else is running in the background.
Since the N4 is sending data to my laptop at available bandwidth, it seems the bottleneck is with the N10, or how the N4 is set to interact with another android device.