You won't find a 3S 8000mAh pack that will fit in those battery trays. And actually, scratch those 6000mAh packs off the list too. They're a little too tall. The Polyquest/PolyRC 5000mAh 3S packs will fit though. They are not in stock here at RC-Monster, but they are available here:
PolyRC PQ-5000XP-3S
http://rclipos.com/PolyRC25C.htm