You can simply pipe top's output to a file using something like cron. There is a very good tool for boot times though integrated into systemd. Call it using `systemd-analyze`. It has a lot of subcommands you can check by `systemd-analyze --help`.

Also, if you'd like to compare performance degradation over time, NixOS is a good choice to run because it can simply rollback to old configurations and you can see what changed.