Do I need a new catalytic converter or just a new oxygen sensor?

I need some help analyzing some data I collected from my 2007 Honda fit using my OBDII scan tool and the Torque app (See images). For some background, my car came up with a P0420 code (Catalyst System Efficiency Below Threshold) after my car experienced a series of massive misfires. To fix the misfiring problem, I replaced all four spark plugs, all four coil packs, did a valve adjustment and replaced the upstream oxygen sensor (the sensor ended up being the main culprit).

Anyway, the problem I am having now is a P0420 code.

I am trying to determine whether a new converter is necessary. If you look at the images below, you will see that at idle, 1500 rpm and 2500 rpm the upstream O2 sensor is describing a nice waveform that averages about 0.45 volts. In the same instances, the downstream sensor is showing a relatively flat line around 1 volt. This is indicating a properly functioning catalyst.

On the other hand, the last two images seem to suggest a broken downstream sensor. I recorded data on engine start up. The strange thing about this data is that the downstream sensor is showing a flat line even though the converter is less than 300 degrees. The downstream sensor should mimic the upstream sensor when the converter is at these low temperatures. Also, when the vehicle is in stop and go traffic, the downstream sensor is showing a lot of noise. I'm not sure what explains the pattern in the last image. The downstream appears to be moving in an inverse fashion with respect to the upstream sensor.

Any thoughts on this? Thanks!