Doom 3 initially shows the overclocked low-cost system in a close second-place position behind the overclocked high-end system, beating its base speed. This is something we predicted earlier, as few games are even so much as dual-core optimized, let alone four-core. We've already proven the low-cost configuration's E6750 is a superior overclocker to any of its four-core siblings when provided enough cooling, so that even getting close while using a cheaper cooler is going to put supreme value on the lower-priced solution. Topping that with the fact that Doom 3 is "CPU bound" at all but the highest resolutions when the "eye candy" is off, and it's easy to see why the overclocked Core 2 Duo configuration earned second place even with its slower, single graphics card.
Turning up the heat with 4x Anti-Aliasing and 8x Anisotropic Filtering solves the above dilemma by putting the cheapest system at the bottom where it belongs.