Clockspeeds mean nothing - we don't have the exact number of calculations the GPU or the CPU can pull off per cycle. We only have estimates based on the basic versions of the components, not the results of the modified hardware, and it was modified for Nintendo. We won't have reliable benchmarks before the 3DS is hacked, really.
We know the polygon-pushing power of the GPU thanks to data on DMP's website. Granted we don't exactly know the differences between the 2008 or 2010 models (3DS likely using the latter one) and we don't know the extent to which Nintendo modified it but we do know enough to rule it as being roughly in the same general ballpark as the Wii.
That's all great and dandy, but the 3DS renders at a 400x240 resolution (displayed times two, with or without the 3D effect, but the 3D actually isn't a lot of extra computing - it's the same scene with some slight alteration and AFAIK it doesn't need extra rendering. Some exceptions (non-3D games) apply) while the Wii's using 640x480 (with some exceptions), so the fact that it's a straight-up port doesn't mean that it's hasn't been greatly downscaled - you just can't see that due to the smaller screen.
Yeah, you're right about the 640x480, my bad, I misread the specs sheet. As for the 3DS, it's effectively 400x240 displayed twice - you need twice the screen width to display something in glasses-free 3D, and the width of the 3DS's screen is 800 pixels. Since there are no transitions while you change from 3D to non-3D mode, it's fair to assume that the resolution does not change while you use the slider... but hey! I'm just guessing here.
That's correct. Both in 2D and 3D mode, the 3DS prepares two 2D pictures, one with slight alterations (if in 3D mode), each is 400x240. It interlaces them in a vertical fashion, creating one 800x240 picture, then each vertical line goes through its respective paralax slit and finally to either the left or the right eye. Meaning, the physical screen is 800x240, but it displays two 400x240 pictures, one for each eye.
