That's the catch. Given how things have been described in the pass, a notch above the 360 can mean up to "not quite current high end". Add minimal RAM and CPU differences, and you got your "a notch above 360".
Tu put things into perspective:
Xenos: 48 shaders, 16 TFU, 8 ROPs
HD 4350 (Super low-end R7xx GPU): 80 shaders, 16 TFU, 4 ROPs.
HD 4650 (Low end, gaming grade GPU): 320 shaders, 32 TFU, 8 ROPs.
HD 4870x2 ("family" highest end GPU): 1600 shaders, 80 TFU, 32 ROPS.
Keeping that in mind, I don't see an scenario where the GPU is not considerably more powerful than the 360's.