Benchmark Results: Left 4 Dead
Even more so than Far Cry 2, Left 4 Dead is very platform/CPU-dependent. In this case, the extreme dependency yields a fairly interesting chart when AA/AF aren’t being employed.
First of all, it’s interesting to note that Core i7 holds onto that slight advantage, even with a single Radeon HD 4870 X2 in play (and all platforms enjoying a full x16 link to the graphics subsystem). Core i5 falls just slightly behind, followed by the Core 2 Quad system and Phenom II setup. It looks like the theoretical advantage i5 held in 3DMark Vantage isn't going to pan out in actual gaming.
Tossing a second card into the mix utilizing CrossFire technology does absolutely nothing for performance. If anything, there’s a one or two frame penalty at the lower resolutions, which the Core i7 suffers as well (so it’s probably a result of overhead rather than a consequence of dividing 16 lanes into two eight-lane links for three of the four platforms).
Because these configurations are so massively processor-bound, adding 4x anti-aliasing and 8x anisotropic filtering doesn’t do anything to hit performance at 1680x1050 or 1920x1200. There is an impact at 2560x1600, though, which makes this one setting an interesting point of comparison between the four different architectures. Again, we’re looking at red bars-only.
Core i7, Core i5, and Core 2 Quad achieve the same results at 2560 with one 4870 X2. The i7’s twin x16 links help it get the most out of a second card, while i5’s architecture leads to it placing second at the same resolution when another 4870 X2 is added. The Core 2 Quad’s speed-up is the smallest, amounting to just 8.5 frames.