the PIC is specified to run at up to 64MHz so expecting it to run at 80MHz might be a bit of a stretch.
Pretty much what I raised back in post 2. My part ran at 80 using an external clock+PLL, but that doesn't mean much.

Ceramic resonator, like crystal oscillators
You mention that crystal oscillators have logic-level outputs, so I think in your comparison a resonator is closer to a plain crystal (but as you mention they usually include the caps).