How to measure time taken for a Feeds processing (benchmarking)?
The Ultimate Cron module will tell you how long the import takes and keeps track of time for each feed import.

In your feed Basic Settings, for Periodic Import, make sure you set it to As often as possible.

In Ultimate cron, jobs tab, Remember to run the scheduler cron job first, then the Feeds cron jobs

Once you have a number, you can manually do the math on how many nodes per second.

Note: the cron run speed will vary based on your server machine. A more powerful machine will get the cron job done quicker.