I know my 750ti worked without needing drivers in macOS, but I think it needed some fiddling with clover. 780 might not work out of box, but I think it will work the web nvidia drivers.
I'd probably put passthrough on USB and use a USB-dac for audio and add some decent bluetooth hardware for handoff, keyboard, mouse/touchpad, etc. I'd really like to have zvols underneat passed to the macOS-machine, I suppose I would have to use a HFS-sparseimage or similar for primary OS disk, but it would be nice to mount the zvols directly via OpenZFS for additional partitions. I would love to leverage LZ4 for document storage etc.
Regarding your first question: I have tried virtualized and bare metal macOS (hackintosh) and I would recommend not virtualizing it if it's gonna be your primary workstation. Currently my main workstation is a hackintosh after trying first using it in a VM.
Virtualizing works, but under a VM there are several minor annoyances here and there that might drive you crazy (most of them are UI related, some app crashes, etc.). It would be perfect for example for a xcode build server. thought. YMMV!
With GPU pass through, pretty much performs the same too... I've maybe seen a 5% performance hit at most after running some benchmarks. I also passed through an NVMe drive directly to the VM which avoids having to use an emulated storage controller.