Uploading a month of history from two IoTaWatt during testing I was getting 240 measurements/sec and the rPi didn’t seem to be the bottleneck. Both IoTaWatt were uploading at their max rate.
That’s the ALPHA software. Heads up, it’s going to change over the next couple of days and break your setup.
The good news is that with the new release, you can easily upload your data again in the new format.