I have no idea what Z64 is, but PJ64 has pretty high compatibility (I used to have a doctor v64 for my N64 so I have complete PAL/NTSC-U/NTSC-J romsets), I only have a AMD turion dual core RM-70 2.00ghz, 3GB ram, and GeForce 8200M on this laptop and have never experienced any game breaking glitches.
Daedalus x64 on PSP is a pretty good emu, and Wii64 shows promise of not only emulating but also enhancing : http://emulatemii.com/wordpress/?p=431
That’s right, high-resolution, custom texture paks are now supported on the Wii using Wii64! Of course, this is still Work-In-Progress, but we’re nearing completion.. Expect a release after this feature is complete. We feel like this is where homebrew emulation on the Wii can really shine and provide an enhancement that Nintendo is not able to offer with their official software.