Xbone Jaguar 8-core x86 CPU @ 1.75 GHz: 112 Gflops
360 Xenon 3-core CPU @ 3.2 GHz: 115 Gflops
There's a chance that SIMD-intensive code (read: VMX128) brings Jaguar down to its knees. AFAIK, they recompile PPC code to the x86 equivalent.
The Xbone GPU is stronger than the 360 GPU though (1.31 Tflops vs 240 Gflops), so it makes sense that GPU heavy segments (i.e. cutscenes) run at a steady 30fps via V-Sync easily.
Jaguar is not that bad, it's just that it wasn't designed to excel in floating point operations, hence the opcode translation will never be perfect performance-wise. That's why we have GPGPU these days.
It would be really cool if they could convert VMX128 code to GPGPU code. If that's doable, then perhaps PS3 (read: Cell SPU) emulation could be feasible as well.