colorado.rob, well... but everything changes and progress does not stand still
So, let's say 8 bit is not reachable for 10-20 GHz sampling rate
AD9213
fIN = 4000 MHz ENOB=7.8 Bits. Does not qualify as "reach 8 bits".
sure, taking 10.25GSPS/2.56 and ENOB at that freq you definitely right, 7.8 is not 8, even if it close to it.
But one can make it equal, assuming that ENOB will increase with lower sampling rate:
10.25GSPS > 10GSPS, so 10.25 - 10 / 10 = 2.5%
8 - 7.8 / 8 = 2.5%