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the fill power of your jacket doesn't indicate warmth so much, more the quantity of said down...it is a better indicator of how light/small your item will pack.
Two jackets could both be 800 fill, just with a different quantity of down in each one. More 800 fill = warmer.
this mid layer I use every day at the moment (under a massive parka jacket): http://www.patagonia.com/ca/product/mens-down-sweater-jacket?p=84674-0
has the same down as this: http://www.patagonia.com/ca/product/mens-special-edition-fitz-roy-down-jacket?p=84550-0
on its own the sweater is no way warm enough for the cold temps, but the fitz roy would be.
800 fill power for summer camping?! You will def be warm!