Another 2 boxes arrived and I think the following statement is close to reality:
IFDS would be like DP5, there should be on average 3 Lv X in each box. (Charizard is counted as the Lv X category, like Yata pointed out, if you get Charizard, chances are you only get 2 other Lv X) And of course, there is 1 key holo card in each pack (except the one that you pull Lv X), these would be cards like Torterra, Infernape, Empoleon, Giratina, Mismagius, Raichu, Abomasnow, Sceptile, Dusknoir, Shaymin, Lumineon...etc.
Further more, I saw some shinning common cards. In 1 of the boxes, I pulled a Drifloon (commno card coding, black circle) that has a plastic coating. It has some holo stars or is it diamonds? I have only collected Pokemon cards for a short period of time and I have not seen these types of cards before. Maybe some of you would know what it is. It is just very nice to hold it in your hand. What a well made card!
For me, I think the Japanese boxes are worth the money. Nothing against PUSA, but the quality of some of the English reverse holo and holo cards are just not desirable. So many times I pull reverse holos (directly from packs) with one side brighter than the other or a tiny band or bands of shinny verticle strip on the card. It is just annoying. (It is not the design as I have another copy of the same card and it does not have that extra 'shinny' feature!)
Another praise is for some of the Japanese packaging, you can open their blister packs without any sharp tools. They loosen one of the corners on purpose, you peel the plastic and you are done. I was never able to open English blister pack with my hands alone. The Japanese 'theme deck' cases are also a joy to open, you can basically put the whole case back the way it was, for English theme decks, once you remove the wraps, you would have to find a separate container. These just shows that the Japanese products do attend to details and I enjoyed it.
Thanks to all who shared their information and it had helped me to make some quick decision last night.