PCI Express & CrossFire: Scaling Explored

Test Settings

While many of our test games show enormous performance gains from higher clock speed, none have shown significant improvements in the transition from two to four cores. Thus, we used a dual-core processor that usually overclocks beyond 4 GHz on air cooling. Intel’s Core 2 Duo E8600 is probably the best gaming processor owners of LGA775 motherboards can hope for their motherboards to support because it starts out as Intel’s highest-frequency model and is easily pushed beyond the speeds other processors can reliably run.

Overclocked to 4.0 GHz at FSB-1600, our Core 2 Duo E8600 required good RAM to achieve optimal throughput. Unfortunately, the oldest chipset in today’s line-up wasn’t designed to support DDR2-1066, and using the DDR2-1000 setting resulted in severe instability. Without the ability to increase memory speed, we instead settled for tight CAS 4 latencies at DDR2-800 and 2.00 volts. Crucial’s Ballistix DDR2-800 4.0 GB dual-channel kit worked perfectly.

With the support hardware in place, it was time to pick graphics cards. Though the targeted upgrade market of this piece will likely favor lower-cost HD 4850 or HD 4830 based graphics models, the HD 4870 allows us to test the limit of motherboard differences when using the same architecture as those two high-value solutions. A pair of Gigabyte’s GV-R487-512H-B graphics cards suited our testing needs well.

To further examine graphics performance differences, we added Race Driver GRID to our regular selection of benchmarks.

Because different generations of chipset support different bus speeds, we also included Sandra’s CPU and memory bandwidth benchmarks to gauge the effects chipset overclocking had on performance.