"How did you configure your Belkin AC1600? I bought one, and it doesn't seem any faster than my old Asus RT-N12."
A change in router is not going to "pump up" your download/upload performance unless the router was a choke point in your network to begin with.
Baseline speed tests need to be run to determine if your system is operating within normal parameters for your platform (HN7000s, HN9000, HT1xxx) and plan level.
These initial tests need to be performed with a single computer connected directly to the modem to reduce the number of variables to the absolute minimum.
Once that is done the tests can be repeated with the router connected and compare the results.
You do have to keep in mind that the number of connected devices and the type of their activity will affect speeds due to a number of reasons such as QoS being enabled, QoS type and any router enabled load balancing and frequency shifting features.