If you are worried about the screen tearing, I can tell you that it is possible to write software that fixes it.
The genesis/mega drive emulator on the wiz is absolutely amazing and has a 'diagonal tear' fix option that completely removes any tearing. Technically it is at the cost of some performance, but I can tell you that even with it on (and my wiz set to to 700 mhz) the framerates on genesis games are perfect... sega cd too!
Mame for the wiz also has a screen tear fix that works great on most games, but unfortunately it doesn't work with neo geo titles (the graphics are shifted around the screen improperly, although it actually works right if you rotate the screen... I hope this could get fixed on a future release). There are also great tearing fixes with gameboy and gameboy advance emulation (the gba emulation is really nice too). I'm hoping that temper (the pc engine/turbografx emulator) can add a screen tear fix in the future. I'm not sure if there are other emulators that have this fix, but more may come.
One other thing to keep in mind is the ghosting on the psp screen and the controls. I've never been a big fan of sonys dpads and I believe the controls on the wiz are much better for emulation of older titles (thankfully they went with buttons and not the dual dpad design). The wiz screen is the perfect resolution for many older titles since it perfectly matches the mega drive and neo geo resolutions so no scaling needs to be done and the image quality is really much much better than the psp. The psp 3000 does have a nicer screen than the previous psp models, although it would be harder to find one that runs emulators. I can tell you that I have a wiz, ds, psp 2000 running custom firmware, and a psp 3000. When it comes to emulators I almost entirely use the wiz because the screen is so nice for them. The oled almost gives you a crt look, but much sharper than any crt you would have had years ago. Also, before you go to the psp, you might want to look at ds emulation. There are surprisingly good emulators on the ds of the nes, sega master system, pc engine, genesis, and even neo geo (although because of scaling issues if you want the image to look decent than you lose some of the image on the neo geo, pc engine, and genesis emulators because the ds screen resolution is lower than these systems had). Hope that helps.