Earnings calculator (Update 2024-04-14: v13.4.0 - Additional info on uncollected garbage and unpaid data - Detailed earnings info and health status of your node, including vetting progress)

The months you mentioned did indeed see surge payouts. Also keep in mind the escrow being held back in the first 9 months.

As for performance, you might want to look at this thread.

The script used in that thread can be found here.