Open has long ceased to be a good metric, as all mail providers like Gmail automatically open the email to check for spam and trackers. So that often gets recorded as an open and the open rate often shoots really high. So the first open is not a reasonable metric.
You can rather optimize for response rates. That is the true signal that a human has actually opened the email and message resonates with them.
If you do have the pixel in, an interesting metric is the emails with more than one opens, which shows the reader is engaged.
