Best airframe for A123 cells?

[redgiki]

I'm currently flying a T-Rex 450XL HDE, a Raptor 30, and a Kyosho Concept 30 (on the bench, I think I'm going to dump the airframe and put the electronics in something else). I want to get into a bigger heli, and despite the weight penalty, I want to do so using A123 M1 cells. I will have 20 cells coming shortly with which to build a pack. I only plan on one pack at the moment, and will be charging it in the heli.

So here's the question: If you were to build a single pack from (up to) 20 cells, what would you recommend as the ideal airframe and power system? I've ruled out the T-Rex 600, because it is difficult to situate an arbitrary-size A123 pack and have the CG remain in balance. I'd prefer something where the battery has some room to slide fore and aft underneath the rotor.

The Raptor E620 seems like it might be a good choice with the lower frame upgrade.

What else are people happily flying on A123 with reasonable power-to-weight and flight time these days?

[Big Fil]

I like the way the battery tray is setup on the E620. Not sure if there is enough room on a Rotorwerks 600 frame but you ruled that out already. The E620 sure looks nice and flies well from what i've witnessed.