Results: 3DMark And PCMark
Although it's armed with a discrete GeForce GPU, the IdeaCentre Horizon is decidedly limited to mainstream gaming. With that said, the performance of its low-power dual-core host processor doesn't help the large all-in-one's 3DMark score, evident from the Physics sub-test.
PCMark similarly exposes the performance deficit of the IdeaCentre's 5400 RPM notebook hard drive. The competing XPS, which isn't portable, benefits from a 3.5" disk and a solid-state cache.
The fairness of this comparison largely depends on what you want from an all-in-one PC. Lenovo is using a low-voltage CPU, an entry-level GPU, and a laptop hard drive in the interest of making its integrated battery useful. Dell charges $1000 extra, employs faster hardware, and sticks to a more conventional desktop paradigm, where you keep your PC in one place, plugged in to the wall.