There seems to be no mention of a dependency between Fif and realisable BW for the AD6676 in the datasheet, although this probably exists, directly or indirectly.
What are the specific BW restrictions at Fif=70MHz? Lext would probably have to be 200nH and Fadc=2GHz. How close to 0MHz or 1MHz could we get the band? Are there any other factors affecting performance at this bottom end of the Fif range?
PS. "the fine QDDC provides 10-bit tuning resolution" on pg. 39 of rev. A datasheet should probably read "8-bit".