Well, the good news is PROJECT_RESOURCES is totally ignored in 8.0+, so it should be safe to remove it. You’ll need to do some surgery on a gateway backup - you can open the .gwbk as a zip, extract the config.idb, drop the PROJECT_RESOURCES table via sqlite, then pack it all back together.
Obviously, keep an unmodified .gwbk around to restore back to just in case, but that should be a pretty safe operation if you’re familiar with SQLite. I can’t guarantee it’ll do anything about your core CPU usage issue, but it might be interesting to try separate from the upgrade.