Tracking Historical Peak Transfer Rate (for SQM configuration)

Hi, I've been watching the "Realtime Graphs" in LuCI and like the "Traffic" tab which shows the peak Mibit/s up/down over the last three minutes.

I've setup luci-app-statistics with the collectd-mod-interface plugin which lets me track the up/down traffic over time. However, the data shown with collectd doesn't match the peak data shown on the "Realtime Graphs". I believe this may be related to collectd only tracking at 30 sec intervals. Does that mean that collectd is only collecting the average throughput over each 30 sec interval?

I recently setup SQM (cake) and would like to track how close I'm getting to the configured bandwidth limits. Does anyone have advice for how I can collect historical peak up/down transfer rate? Or if you have any other advice for tracking how close I'm getting to reaching my configured SQM limits?

Thanks for the help!