PCI Express And CrossFire Scaling: Is P55 Good Enough?

We hear from nearly everyone in the comments section that the LGA 1156 platform, which has 16 PCI Express (PCIe) 2.0 lanes provided by the CPU's on-board controller, is destined to be nothing more than a mainstream product for gamers using, at most, a single graphics card. A slow DMI interface linking the CPU to the P55 Express PCH at PCIe x4 bandwidth certainly doesn’t help bolster the platform’s performance credentials, causing many to question why Intel would add the Core i7-870—a $540 part—as one of only three launch-day Lynnfield processors. Certainly nobody would drop such an expensive component ontp a “mainstream” motherboard. But that was exactly the option Intel was hoping many builders would choose.

We’ve since found the Core i7-870 to be an excellent (albeit pricey) part, with clock-for-clock performance in a dead heat with LGA 1366 processors, better Intel Turbo Boost ratios, lower average power consumption, and superior overclocking of up to 4.3 GHz on air cooling. All of these great advancements cause us to ask whether the Lynnfield family of Core i5 and Core i7 CPUs might be wolves in sheep's clothing. 

Is the limit of 16 PCIe lanes really that much of a hindrance? Is the performance difference between eight and 16 lanes really big enough to dismiss CrossFire from the list of the platform’s capabilities, as some have suggested? Is the x4 slot often added to $200 X58 motherboards really better than those of similarly priced P55 products?

Those are all great questions, and we begin our journey with an examination of slot performance, comparing the performance capability of x4, x8, and x16 slots on both the P55 Express platform and the X58 Express that came before it. Great pains have been made to ensure that everything else is equal throughout each test, as described in our configuration page.