PCI Express And CrossFire Scaling: Is P55 Good Enough?

Test Configuration

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Test System Configuration
LGA 1156 CPUIntel Core i7-870 (2.93 GHz, 8MB Cache) O/C to 4.00 GHz (20x 200 MHz), 1.388V
LGA 1156 MotherboardEVGA P55 SLI E655, P55 Express PCH BIOS A39 (10/23/2009)
LGA 1366 CPUIntel Core i7-920 (2.66 GHz, 8MB Cache) O/C to 4.00 GHz (20x 200 MHz), 1.434V
LGA 1366 MotherboardEVGA X58 SLI E758, X58 Express IOH ICH10R, BIOS SZ2Z (11/30/2009)
CPU CoolerThermalright MUX-120 w/2,500 RPM Fan
RAMKingston KHX2133C9D3T1K2/4GX (4GB) DDR3-2133 at DDR3-1600 CAS 8-8-8-24
Graphics3 x Diamond Radeon HD 5870 1GB 850 MHz GPU, GDDR5-4800
Hard DriveWestern Digital Velociraptor WD3000HLFS, 300GB 10,000 RPM, SATA 3 Gb/s, 16MB cache
SoundIntegrated HD Audio
NetworkIntegrated Gigabit Networking
PowerCorsair CMPSU-850HX 850W Modular ATX12V v2.2, EPS12V, 80 PLUS Gold
OSMicrosoft Windows 7 Ultimate x64
GraphicsATI Catalyst 9.11
ChipsetIntel INF

We performance-matched our LGA 1156 Core i7-870 and our LGA 1366 Core i7-920 exactly, using a 20x multiplier, a 200 MHz base clock, and no Turbo Mode or C-State manipulations that might have otherwise altered our test results.

Thanks to the similarity between it and the Cogage True Sprit, Thermalright’s MUX-120 required only a bracket change to go from our i7-870 to our i7-920 platform. However, a faster fan was required to support the i7-920’s higher-voltage overclock.

We used one of our two sets of Kingston overclocking RAM to put both platforms in dual-channel mode. Having both systems configured equally is essential when attempting to narrow performance differences to slot configuration.

Diamond Multimedia supplied the three cards needed to perform all of today’s tests.

With 36 lanes on the northbridge, X58-based motherboards typically offer either x16/x16/x4 or x16/x8/x8 pathway sets, depending mostly on price. Cheaper boards lack either the needed lane switches to support x8 mode or x16 capability on the second slot, while more expensive boards typically don’t have a x4 slot in the proper location for installing a video card. Measuring x4 bandwidth on our x16/x8/x8 motherboard required the addition of an insulator, as previously discussed here.

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Benchmark Configuration
3D Games
CrysisPatch 1.2.1, DirectX 10, 64-bit executable, benchmark tool Test Set 1: Very High Details, No AA Test Set 2: Very High Details, 4x AA
Far Cry 2Patch 1.03, DirectX 10, in-game benchmark Test Set 1: Ultra High Quality, No AA Test Set 2: Ultra High Quality, 4x AA
Tom Clancy's H.A.W.XPatch 1.02, DirectX 10.1, in-game benchmark Test Set 1: Highest Settings, No AA Test Set 2: Highest Settings, 4x AA
S.T.A.L.K.E.R. Clear SkyClear Sky Benchmark version Test Set 1: Ultra Preset, DX10 EFDL, No AA Test Set 2: Ultra Preset, DX10 EFDL, 4x MSAA
World in ConflictPatch 1009, DirectX 10, timedemo Test 1: Very High Details, No AA / No AF Test 2: Very High Details 4x AA / 16x AF
Synthetic Benchmarks
3DMark VantageVersion: 1.0.1, GPU and CPU scores
Thomas Soderstrom
Thomas Soderstrom is a Senior Staff Editor at Tom's Hardware US. He tests and reviews cases, cooling, memory and motherboards.
  • kirvinb
    I wonder does the same go for 790gx vs fx
  • gilbertfh
    I just ordered myself an ASUS P7P55D-Pro and didn't understand the difference... If I spent $1200 on video cards to go in this bad boy expecting it to test at higher performance that I will never be able to see by the naked eye it may have been a bigger deal(but it isn't).
  • gkay09
    It is pretty logical to go the X58 route if you are planning for more than 2 cards...
    Only 2x HD 5970s would have significant bottleneck with x8x8 config of the P55...for rest of the cards, the x8x8 still would suffice...
  • jsc
    For most of us, it looks like the P55 is the way to go for a gaming machine. I was a little surprised at how well two X8 channels did.
  • neiroatopelcc
    Does it make a difference for the motherboard wether or not all slots are populated when we talk energy? Each pcie plug is supposedly able to deliver 75W to the cards right? so at 3 cards that's quite a bit of power. In addition it has to deliver what, 140W? to the 4ghz cpu .... remembering an earlier article detailing failed boards because of inadequate vrm's I just have to wonder if a higher power draw on the pcie connectors would make a difference in sustainability with such an oc? I mean at some point I would assume a board can draw more power than the atx connector or the power plane can handle?
  • a4mula
    pcie 2.0 supports up to 300w (1.1 was 75w). The 5870 draws about 170w at load. This was the reason the 5970 was scaled back to 5850 speeds. Overclocked 920 @ 4.0 is going to draw about 250w. i5 750 (@ 4.0) on the other hand draws about 150w.

    For awhile now it's been known that the p55 will run an 8x8x crossfire within close proximity of it's x58 16x/16x even on 5870's. The only real question that hasn't been seen is the quadfire 5970's and a trifire 5970+5870. Publish that and you'll garner my attention at least.
  • neiroatopelcc
    300w ? but why then would new cards still ship with pcie6 and 8 connectors if the cards actually could make do with the pcie supplied power? I mean, sure for pcie1 support, but won't they still bitch if one was to not plug em in under pcie2?

    ps. 150W is also a lot for a processor designed for two digit numbers. Is there some kind of list somewhere of which motherboards support how much vrm power, or how many phases generate how much wattage or whatever can be used as a guideline?

    Gonna upgrade the p35 to p55, and I've never been one for stock speeds...
  • jennyh
    The gap is just going to increase with more and more powerful graphics cards. We're talking 1-2 years and 8x will be performing just like 4x is now.

    8x Pci-e lanes should now be considered a drawback when purchasing new hardware.
  • notty22
    "8x Pci-e lanes should now be considered a drawback when purchasing new hardware."

    They just proved it was NOT a drawback with two 400 dollar top tier gpu's.
    Someone that advocates not upgrading the rest of their motherboard specs to the current high performance components such as DDR3 and the fastest hypertransport speed should not worry about THEORETICAL pci-e bandwidth.
  • baracubra
    Yeaaaaah! I've been waiting for this article for quite a while now, this clears up a lot of speculation! I hope you guys do a follow-up article to test whether two 8x,8x are enough to support 2x 5970's....

    If this article had come out 2 weeks ago, I would have upgraded to an i7-870 and 2x 5870's, but now that we know Fermi is arriving in Q1 2010 I'm afraid i'm gonna have to wait. . . again -.-

    Oh well, that's why we love the PC market, always advancing :)