Um...what? That doesn't make any sense. The 240p test suite is a completely separate homebrew program, it has nothing to do with any emulator at all. Every emulator (regardless of platform) is going to have its own degree of input lag that can't be tested outside of the emulator itself.
That said, I can assure you that VBAGX has a considerable amount of input lag compared to mGBA. How much exactly in milliseconds is anyone's guess.
In this context there are two sources of Input Lag: lag cause by the display up-scaling a 480p video source to it's native resolution, and the lag inherent in the emulation itself.
For example when running the Wii version of the 240p Test Suite directly via the Homebrew Channel, the Manual Lag Test gives me an average of 1.2 frames of lag, meaning that 1.2 frames of lag is caused by my TV having to upscale the Wii's 480p video signal to its native 720p.
When I run the SNES version of the Test Suite through SNES9XGX, I get on average 2.5 frames of lag, meaning the emulator itself has 1.3 frames of input lag.
1.2 frames is roughly equal to 20 milliseconds. Generally, 30ms or less of lag is considered the acceptable limit, where input lag won't be noticeable and affect gameplay to a perceptible degree. SNES9X has a total of about 41ms of input lag, which is enough to be noticeable in action heavy games like Mega Man X, in which I found dodging to be more difficult then it should have been.
