Fable 5: I give it work, it tells me things that are true and that make sense, it does good work.

Opus 5: I give it work, it makes false statements and draws weird conclusions, I correct it and get it on the right track, it thrashes around but gives me something working though usually buggy.

5.6 Sol is probably on par with Opus 5 on ability but at least it doesn't waste as much of my time.