Since we have the curator of the Sorabji archive as member here I cantell you that Powell uses the newest edition with all the corrections.
I will have to find a copy of that. Thanks for the confirmation of my ear hunch and the tip 
Good luck with that. I suspect it will be quite some time before such an edition is available. Cross-referencing the manuscript, the original publication, the "working copy", and those portions of the pre-publication proofs that are currently available is an incredibly time-consuming and often frustrating experience.
My understanding is that Jonathan Powell has been adding some corrections into his own copy of the score, as well as re-setting certain passages from the fugues for clarity, but I'm not sure this is as yet comprehensive; I'm pretty certain I detected a number of mis-readings still remaining, judging by that performance (yeah, I know I'm being an ungrateful, nitpicking sod - sorry

)
As well as sorting out the actual notes, the whole score ideally needs to be completely re-typeset at some point. There are passages where the layout, alignments, registers, are simply wrong, and plenty more where the often awkward notation could be made much more readable, thereby reducing the potential for misinterpretation. I would also argue that there is at least one place (var 33 from the passacaglia; page 167 in the publication) where it might be useful to make an editorial ossia available to the performer. I'm inclined to believe from the inconsistency, and from seeing similar problems in Sorabji's other scores, that the truncated theme in the first bar is a compositional oversight.
A job like that is likely to take a
minimum of a year to do with any competence. I don't believe for a second that JP has the time to undertake such a task, and I'm not aware that anybody else has started.
I'd like to think that the incorrect notes at least will completely sorted out by the time JP takes the work to the studio, but I seriously doubt you will see the publication of anything that could claim to be a "corrected edition" before that time.
As for comparing his performance of Part I with that of Madge and Ogdon, I would say that Powell's performance so far has been well worth the wait. I particularly enjoyed his approach to Fugue II; it was far more coherent than the versions of Madge and Ogdon - less of a scramble in places.
Best,
Simon