[gcwebbyuk]

I currently have a Giga P67A-UD4 board a GTX570 for my main screen, and an HD5450 for my second.

Does running these cards even as completely separate (non SLI or crossfire) cards still slow down the PCI bus so that the they run at 8x?

I am due to replace the board (it is an original Sandy Bridge board) and considering a swap to an Asus P8P67 DELUXE board. This has three PCI-E slots, and the spec states:
2 x PCIe 2.0 x16 (single at x16 or dual at x8/x8 mode)
1 x PCIe 2.0 x16 [Black] (at x4 mode, compatible with PCIe x1 and x4 devices)

Am I right in thinking if I use slot 1 for the GTX570 and slot 3 for the HD5450 they should both run at 16x?

[Knufire]

At x8, you won't see a performance drop. But yes, putting in the card will lower it to x8/x8, but it isn't that big of a deal.
Two questions:
1. Why the need for two separate cards, the GTX570 can drive two displays
2. You could sell the B3 board and get a Z68 motherboard, then use the iGPU to drive the second display if you're worried about bandwidth.