Would it not be better to use for the ADC section several ADCs with better THD parallel, as it is not intend to use the analyzer for analyzing MHz signals anyway? E.g. several LTC2378-20 if you want to stick with SAR ADCs.
Oversampling, as well as using several in parallel equally reduces random noise of the AD, but has no substantial effect on non-random distortions like the THD.
Oversampling has the advantage that the analog anti aliasing filter is less demanding.
Parallelizing gives you a better "bit resolution".
Moreover you still have the option to use the multiple ADCs interleaved, if you want to provide a bigger frequency range.
Oversampling, as well as using several in parallel equally reduces random noise of the AD, but has no substantial effect on non-random distortions like the THD.
Oversampling has the advantage that the analog anti aliasing filter is less demanding.
Parallelizing gives you a better "bit resolution".
Moreover you still have the option to use the multiple ADCs interleaved, if you want to provide a bigger frequency range.