How powerful was Kirak Infil'a?

Given his performance against Vader, where would you rank him among the other Jedi of that era?

He was said to be the most powerful Jedi that Vader had faced up to that point. So he should be above Kenobi, and probably in the Mace / Dooku tier.

If the quote is legit he is above Kenobi.
The problem is that we don't know for sure if the quote has any canon value since it was from the publisher (marvel). From what I know this kind of quote is not verified and approved by the story group.

^ The quote was actually printed in the Darth Vader v1 TPB:
https://i.imgur.com/qoZ8nDr.jpg

So yeah, it should definitely be canon.

Is he also >Dooku?

If he scales above Kenobi, then I would assume that he could potentially be in Dooku's ballpark.

Ya, that's what I'm curious about.

We know Kirak is above Kenobi level, but do we know to what extent?

Hard to say because Kirak didn't do much.

His best feat was probably overpowering Vader's first force choke. But after that he only fought Vader with his suit damaged.