Hi there!
If your itinerary is unchanged, then I can only recommend the 7 day pass to you for your period of travel down to Osaka. As you rightly point out, even then your savings will be small, though you will retain good travel flexibility. A 14 day pass will probably end up costing more than purchasing JR tickets.
However, your final decision should very much depend on what sort of travel you intend to do during day 8-12, and also during your trip to Osaka. For example, excellent day trips from Osaka are journeys to Kyoto, Nara and down to Hiroshima/Miyajima World Heritage Site. Similarly from Tokyo, a highly recommended day trip from Tokyo is to the Nikko World Heritage Site.
If these trips (or trips like them) were included in your itinerary then it would certainly mean a 14 day pass may become worthwhile:
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Narita airport terminal 1 > Shibuya: ¥3,110 (85mins, 93km)
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Shibuya > Maihama: ¥380 (54mins, 26km)
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Maihama > Shibuya: ¥380 (51mins, 26km)
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Shibuya > Maihama: ¥380 (54mins, 26km)
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Maihama > Shibuya: ¥380 (51mins, 26km)
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Shibuya > Osaka: ¥13,750 (210mins, 556km)
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Osaka > Hiroshima: ¥10,150 (104mins, 345km)
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Hiroshima > Kyoto: ¥10,990 (126mins, 380km)
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Kyoto > Tokyo: ¥13,420 (161mins, 513km)
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Tokyo > Nikko: ¥5,630 (121mins, 150km)
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Nikko > Tokyo: ¥5,630 (117mins, 150km)
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Tokyo > Narita airport terminal 1: ¥3,140 (58mins, 79km)
JR ticket cost: ¥67,340 for 12 legs
Also, I just noticed that the link to the JR map in my last reply was broken - here's a working link!.
You can look up precise train timetables and costs at the Hyperdia travel planning website and learn how to use Hyperdia for JR Pass holders through our video blog.
Our Philippines delivery takes 2 business days, so if you were to place your order today, then your rail passes will be with you by Wednesday the 24th - in good time for your trip.
Hope this helps!