Whoa there, don't make such dangerous assumptions about those ADCs. The ADC types in SDS7102 are two channel 500 MB/s (that's real MB/s, not MiB/s) units, which can be set to work as single channel 1 GB/s unit. These aren't Gb/s or kb/s ADCs! I've heard of research in very high speed sigma-delta ADCs which could in theory be used for imaging or datacapture with just one bit, but we're not close to having them in our "simple" oscilloscopes.
Next, in order to get relevant data, for 100 MHz sine wave with bit depth of 8 bits per sample, we need rate of 200 MB/s. This is due to the type of interpolation used, namely the sinc(x) function. The downside of this calculation is that we can get some pretty big problems if for example the start of the signal and the start of our sampling period aren't correctly matched. Basically, we need two correctly placed data points to use sinc interpolation to get a sine wave. I'm not sure how much points we'd need exactly, if there's a mismatch. It should be fun to calculate, so I'll try to get some results and graphs one of these days.
For a triangle, we'd definitely need even more data than we'd need for the "simple" sine wave. I'll try to make some experiments with that too, but I can't make any promises.
The SDS8000 series uses a two channel, 1 gigasample per second ADC, which can be set to work as single channel 2 GSA/s ADC.
In any case, on paper, SDS7102 should be capable of showing data with no aliasing up to 500 MHz and 8000 up to 1 GHz. I did use my SDS7102 go look at spectrum from DC to 500 MHz and the data looks OK, expect of course the high frequencies are severely attenuated. I could make out lower VHF TV channels though. I'll post a picture as soon as I dig it up.
This leaves us with the sample rate=bandwidth*10 rule of thumb, which would be violated in case of bandwidth increase. How big of a problem that would be, I'll leave for someone else to answer
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