Definitely ordering OOTP.
Pre-order price is ~$25.
Still haven't found any definitive audio specs for the others but I'm assuming DD+ instead of TrueHD.

Since Im in Japan I was thinking about it, what made you decide to order from this way and not Amazon in the US? Is there anything different, I was thinking about ordering the set from Amazon in the states, but I already imported GoF, not sure yet what Im doing.

OOTP is a 2 disc set there with more extras and in HD so if they don't fix the US version I will get it there.

Just in case some aren't aware,
when ordering from Amazon.jp, the pre-order price is much cheaper than the regular price.
Once the release date comes, msrp takes over.

Does the Japanese version of OOTP have IME?

Yes to IME. All the bluray focus points, all extras in HD, includes A & E documentary that the US version does not unless something changes.

I can buy the Japan edition but I am worried that it may have forced subs on special features.

I am planning to get the Harry Potter films, at least the latest one, on the Japanese release for a number of reasons but mainly because (1) it's not a combo and (2) all the "extra" extras!
Does anyone know if the Japanese releases of all the Potter films will carry extensive extras (like, possibly ported over from the SD-DVD releases) or if they will be film-only singles?
Whichever, I don't think I"m even going to try for a box set.

They should be loaded. Go to hddvdformat.blogspot.com they should have the info there.

HDDVD blogspot is reporting that the 1st 3 HP movies have been pulled from the Nov 21st release slate. BUMMER.
For the time being I guess this makes the decision easier but will make shipping more expensive.

I just ordered OOTP from Amazon Japan. Does anyone know if 2nd disk is just the same as the bonus disk in the US box set?

Before ordering from Japan please confirm the below

1) Availability of English menu (Catalog titles on Blu-ray and few HD DVD titles come with multilingual menu options).

2) Whether there is forced subs on Special Features.