There is no such thing currently. Therefore B&B 28 in 9.4 continues to be the 3rd most valuable SA DC book, behind the 9.6 and 9.4 copies of Showcase 4.
Would a 9.4 SC #22 top a 9.4 SC #4 right now is the bigger question in my mind. With the emergence of the 9.6 I doubt that a 9.4 SC #4 would come anywhere close to its high price now.
FWIW, I expect SC #22 to eventually end up as #1 if the GL movie franchise does well.
Given that Showcase 4 predated 22 by three important years and is widely regarded as raising the curtain on the Silver Age, I'd say that Showcase 4 in the same grade will continue to elicit higher bids than Showcase 22. And I'm saying this even though Green Lantern is my favourite hero.