My take:
9G at the same speed, they should follow the same trajectory. F=MA, given F comes from lift, A=9G, F will need to be less in the lighter plane (less M), therefore less lift/unit area of wing, therefore less AOA. PPL level aerodynamics teaches me that Vs increases with weight (well, load factor)...
In theory the lighter plane ought to be able to increase the A (>9G), but the pilot will probably pass out. However, the lighter plane should be able to pull 9G at lower airspeed than the heavier one therefore turning tighter (can't remember the equations for circular motion, but the faster it goes, the harder it needs to pull)
Perhaps more importantly, will bleed less energy (less AOA, less induced drag) while turning. Downside is all that unnecessary wing area causing parasitic drag when going flat out in a straight line...
Or, to relate to something more practical; my little sailplane stalls considerably slower than the C150 I'm flying. They both double their stall speed in a tightly banked turn. Double the sailplane's stall speed is a lot less than double the C150's stall speed; so at equal speed / load factors underneath the stall, the sailplane is at a lesser AOA, so I can pull harder and turn inside.
I'd put money on the sailplane to out-turn the C150 at any speed. In fact, it'd probably still be turning when the wings peeled off the little cessna.. but it's designed to a higher load factor
Sure the military folks could give you chapter and verse, this would be right up their street I guess!
<Gliderpilot, PPL in training>
/Mark.