Sabertooth Z77 Video Card Dilemma

I am running an Asus Z77 Sabertooth with a GTX 560tiFTW video card. I am going to purchase a GTX 680 to replace my 560, but was considering using the 560 as the PhysX processor.

To accomplish this I first thought to simply run the 680 in the primary slot and the 560 in the secondary pci-e 3.0 slot. I realized this would bog my PCI-E lanes down to x8/x8 mode, and bottleneck my primary card.

There is a 3rd PCI-E lane on the Asus Z77 Sabertooth, labeled as "PCI-E 2.0x16 (x4 max)" in the manual.

The manual shows the operation modes of all 3 pci-e lanes with single and dual card setups. in both charts, the PCI-E 2.0 slot's operation speed did not change.

Does this mean that I can effectively run a single GTX680 in my primary PCI-E 3.0 x16 slot and run the GTX560tiFTW as the PhysX processor from the PCI-E 2.0 x16 slot with the 680 performing at x16 and the 560 performing at x4?

Most research I've seen doesn't indicate a loss of performance from x4 to x8 when used for a PhysX processor, so if this is the case I don't mind the 560 being "bogged" in a x4 lane if my 680 will run with it at x16.

Someone please confirm this suspicion for me, I need to know if I have to purchase a larger PSU when I order the card to accomadate 2 cards.
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  1. I don't think this would bottleneck the primary. My GTS250 does not take performance from my GTX460, and nor did it take performance form my 6950.

    What is your current power supply? What games are you playing that require Physx?
  2. Arkam City. I have a Corsair TX650, which has enough for a single card that needs 38 amps on 12v rail. I would need an HX 1050 for the required 38 amps per card. And this hypothetical setup is simply to ask if the PCI-E 3.0 GTX680 can run at x16 in the primary 3.0 slot with the GTX560 running at x4 in the seemingly independent PCI-E 2.0 lane.
  3. i dont want to run the 680 at x8, basically.
  4. I don't think it will. And you don't need a HX1050, that's way too much. Probably a good 850W would do the trick. Not saying the HX isnt good. Its a great buy.

    I can't be sure, but I think when Physx runs, it doesnt run the primary card at x8.
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