So this may come as a surprise to some, but the AMD Radeon HD 4870 1GB Quad CrossFire leads in our benchmarks when focusing on the resolution that matters for this hardware (2560x1600).
While driver issues and a lack of other "stuff" like PhysX and CUDA to do matter with GPUs in situations where hardware doesn't scale, the AMD solution leads the GeForce GTX 295 in more benchmarks (Age of Conan, Left 4 Dead, and Far Cry 2), and ties the NVIDIA solution in one title (Fallout 3). Not shown in our numbers is Race Driver GRID, as we have a continuing issue in FRAPS that gets in the way of recording performance numbers with 4-way NVIDIA solutions. We were able to watch frame rate, however, and it was clear that the NVIDIA hardware didn't reach the performance levels of AMD hardware in GRID.
Certainly this isn't a sweeping victory for AMD, and the outcome, because it is close, rests incredibly heavy on the benchmarks we chose and were able to run. Different titles may have produced different results. Thus there is no clear winner in terms of absolute performance. This will depend greatly on title preference. It is worth noting, however, that when Quad GTX 295 leads Quad 4870 1GB, the NVIDIA card comes in at the very top in terms of performance more often than does AMD. But the dark horse in the 4-way focused article is the 3-way high NVIDIA GPUs.
The 3-way GTX 280/285 leads the 4-way GTX 295 in half our tests: it's a wash and it's either slightly cheaper or slightly more expensive depending on the specific flavor. The 4-way Radeon HD 4870 1GB only leads 3-way GTX 280/285 in 2 out of the 6 tests, though it ties in one of them (Fallout 3 again). If GRID were added back in, it's likely the playing field would be completely even on that count.
If you want an added twist, moving from 2-way to 4-way, AMD tends to scale better at 2560x1600 than NVIDIA. Whether that's because of lower baseline performance of the 2-way option and less system limitation at the high end, it's still impressive that the playing field is this even.
So what's the bottom line? Wow ... It's very hard to say that the differentiator is only performance itself. But as we had less trouble with 3-way than 4-way, so our very slight preference for this one is the 3-way GeForce GTX 285. Overclocked hardware will get you even further into the stratosphere. Enjoy the ride.
If you don't happen to have a motherboard that supports 3x double-slot x16 physical PCIe cards, 4-way will have to be the option. In that case, Quad HD 4870 1GB scores points for keeping up with the Joneses, scaling, and bang for the buck. In terms of performance per dollar, which some people may not care about at these top end price points, AMD leads. At the same time, we must consider that heavy investors like things to play with and PhysX and CUDA do add a potential benefit over AMD that some enthusiasts may like.
So who's got the true halo? Who can provide the best highest-possible-end option? In spite of our leanings and recommendations and considerations, It's a wash. This one goes down in the history books as a battle for the high end that will come down to brand preference.