I'm assuming you mean scaled to full screen.
nes - GPFCE is full screen. tearing is noticeable under close inspection, but not enough to ruin play experience.
game gear - Alexkidd2x version v0.6 does not seem full screen, but is approximately 70 to 75% fullscreen. Tearing is worse than nes but not by a lot.
Finalburn alpha - FBA2x is 100% full screen, although I'm not able to say if there is any "bleeding" of the image outside of the screen, I do not expect this though. Almost no perceptual tearing. Although under close inspection, tearing can be seen rarely.
gameboy advance - gpSP is 100% full screen - seems to have mild "graphical distortion" as a result from the style in which it is scaled up to the screen size of the wiz. I personally would be happy with true pixel representation of the gba screen being scaled up without "up scaling" effects like you would see on a giant HD tv displaying standard definition video. If held approximately the distance you would hold an actual gba, this isn't as much of an issue, perhaps this the way the authors intended someone to use their wiz when playing gba games. Tearing is noticeable during drastic fades in and out to black/white or fast scrolling of large parts of the screen, but again, not bad enough to ruin the play experience.
Quake 2 is amazing. Almost zero perceptual tearing. especially spinning and making oneself dizzy, there is no tearing.
All emulators I've tried (of those that I am sure aren't in their earliest stages) are full screen or almost completely full screen and many of them have little to no tearing, and almost all of them have such minimal tearing that it does not ruin the play experience. However, for a time I actually regretted getting my wiz, but over time, I installed so many good emulators with diminished or almost no tearing that I began to forgive the tearing defect. It eventually becomes not a bother at all. Now, the ghosting on previous PSP models, killed it for me. Especially when it came to video playback.
Now, video playback on the wiz is hardly at ipod touch level, but its playback is well enough to be very watchable (for those of us that don't need reading glasses at least.)