if you want very fast data you can try my method UDP streaming the RAW out put from MCP3XXX devices to your server … it works fine and I can sample all inputs at 1/2 second intervals if you like or greater . my device is not the iotawatt but it similar in construction based on arduino format to fit wemosD1 so it interchangeable between arduinos and wemosd1. so you need to modify ino to match yours. I used the emonlib firmware as reference for processing the data locally but you can use iotawatt as reference if you like and build based on that…
the reason I like the UDP push method I can visualize the via oscilloscope and energy monitoring all in the same instant. though currently it operating on a esp I probably convert it to work on wire instead of wifi at some point