So I finally was able to test my MiSTer with a real PVM. I used a VGA to BNC cable, and edited /config/MISTer.INI to disable scandoubler and provide composite sync on the VGA HSync pin.
Happy to say that most cores work really well. For some reason I couldn't get the Spectrum, Apple II, Mac and Moon Patrol to display properly. I suppose Mac and Moon Patrol have non standard video modes. For Spectrum and Apple I'm not sure, I guess that maybe its outputing a 50hz signal? But the TV is supposed to handle it.
Anyway with what works its already great. With a nice CRT the experience is as good as the original machines.