In the oldest showings, he did fight Hercules evenly in hand to hand.

In another old showing, he was powered up by the Celestials and still got beaten by Thor (but that same comic noted that while Ikaris wasn't as powerful as Thor or the Forgotten one, that it was the difference between mighty mammoths, putting Ike in a similar class, if a clear step down).

The Avengers run consistently showed him as a peer to Thor, and had him using his EP frequently, as well as some of the other Eternal abilities. He used his psi to compensate for blindness when he was blinded (I don't remember why he couldn't heal at the time though) for instance.

I'd say overall he's class 100 but not at the top of the level, despite the Hercules match, he doesn't seem to have been quite as strong as Thor, top end fighting ability, flight, and EP. A good match for early post crisis Superman, but outmatched physically certainly by post DOS Supes, though he'd make it a real fight IMO, because ANY class 100 is a threat IMO.