Vincent,
First off make a mockup of the A123 pack to see where you can put it in the plane.

I don't know much anything about the Hyperion motors, but if I was going with an AXI in a Nobler, I would start with the 2814 or 2820. I am not sure what kV you will need with a 5s A123 setup (I would guess somewhere in the 900-1000 rpm/Volt range.  However I think Igor Burger would probably have a better idea of where to start. He may know more about the Hyperion too.

I just recalled that on my original Nobler thread, there was a post from a German modeler on a electrified Nobler. That was a really sweet setup! Here is a link to it. The relevant reply is #34

http://stunthanger.com/smf/index.php?topic=6975.0

I am not sure what kV you will need with a 5s A123 setup (I would guess somewhere in the 900-1000 rpm/Volt range.  However I think Igor Burger would probably have a better idea of where to start. He may know more about the Hyperion too.
http://stunthanger.com/smf/index.php?topic=6975.0

I do not know Hyperion too, but since I know that combo 6s A123 works well with AXI 2826/12 for 5 minutes fligth time, I would say that 5S A123 will work well with AXI 2826/10. Both with APCE 12x6. it will have 20% less power, so you must use slower RPM and it means shorter lines. I fly 20m so if I calculate it witout knowing the model, then 20% power less means rpm 7% lower, so also line length must be 7% shorter to have the same lap time, so I would say lines approximately 18-19m.

One cell weights 70g so whole pack is at 350g plus motor 190g plus esc 50g ~= 600g = 22oz

cells dimmensions are directly in cell name: ARN 26650 ... means diameter is 26mm and length is 650mm :-)