Second test
File transfer. SUT was a PS3 set top box streaming video from Youtube.
Results
The transition from primary to secondary, then returning to primary, occurred without any affect to the A/V stream or the application.
Analysis
Recommendation
Eliminate single points of failure. Right now, both routers share the same power strip and share a single ISP. A used UPS just became available from a family member. A backup ISP is available via mobile phone and WiFi tether, though this solution is not automated.