403: Geekery

After a bit of tinkering (largely undoing my mistakes from my first attempt, before I realized that I was getting sick), I've got the Hercules mainframe emulator running on my laptop. Now I've got to decide which system mode to run it in, and which OS to use. More advanced systems will have higher expectations of my hardware - to the extent that emulating a z/ series mainframe would be pointless without a higher-spec machine. That still leaves me with the ability to get decent performance out of the older S/370 or ESA/390 options, however. The OS options that look interesting are VM/370 or MVS (for the challenge) with S/370, or Linux/390 for the ESA/390 architecture. Opinions from anyone who's even vaguely familiar with this stuff would be appreciated. (And no, I don't know what I'm going to do with it when I'm done.)