Today I'm doing few tests on my 4820K+X79 platform.
The Host is already upgraded to Fedora 23, which QEMU was upgraded to v2.4.1, and the kernel was 4.2.7-fc23
Then, same as previous, using GTX980 as guest VM card. And guest was Windows 7.
Here is my results.
1. Q35 / x-vga=on / without graphic >>> Got monitor but Code 10
2. Q35 / non x-vga=on / with graphic >>> Blank monitor + Code 10
3. Q35 / x-vga=on / with graphic >>> Same as 2
4. i440fx / x-vga=on / with graphic >>> Both monitor and VNC got blank
5. i440fx / non x-vga=on / with graphic >>> BSOD 0x3B
6. i440fx / x-vga=on / without graphic >>> Works
But if using AMD V4800 as guest card then using method 5, it works.
So this may proved that Alex talked about before, it's impossible to make graphic and pass-through GPU exist together.
Only AMD, and NVIDIA card that Quadro K2200 and higher can be as secondary GPU (As I know, it's possible to make VNC (Spice) and monitor worked at the same time on Windows 10, just different resolution).
I'll try to get K2200 if I got enough budget.