Both connections are using WI-Fi?
Wireless connections, by nature, can vary a lot deepening on a number of factors. But even so, a ten to one variation is not normal for two PCs in the same area.
As a control, what happens if you use direct Ethernet cable? If that gives normal results, we can conclude there is a problem with the wireless adapters.
Cheap USB Wi-Fi adapters are an easy way to test out your wireless. Some under $15 work as well as the high price models. Do Google search.
You expect no more than 30 Mbps, so the type N adapter is not needed. The type G is good enough, it can do up to 54 Mbps.