Hi Alexander,
I trust both Fidelity CC7 and Novag CC Super Sytem III (from 1979 as well) are slightly stronger.
But above all, I am pretty sure Applied Concept Sargon 2.5 (aka Boris 2.5), which appeared the same year, is much stronger than Atari Video Chess.
It is indeed stronger than Boris and Boris Diplomat, and slightly stronger than Fidelity CC10 (1978, though).
It is also stronger than some 1980 devices (Novag CC Chess Partner 2000 or CC Pocket Chess).
Not bad at all, so.
MfG
Eric