After lots of reading, I'm finding that there is quite a difference with some Z68 motherboards, when using multiple pci-e/pci slots. 1 card lets you go 16x, 2 cards changes it to both running at 8x.
So question comes, if I'm running two PCI-E cards in SLI that would put me at 8x on each. So what happens when I add a PCIe 1x tv tuner card and/or a pci firewire 800 card (or other pci card). Does that then start taking away from my video cards running at 8x each?
That depends on the board. Some have PCIe bridge chips that give more PCIe lanes so that you can use all of the slots. On the boards that don't have the bridge chip, it wouldn't pull from the graphics cards, but it would disable other controllers on the board.
The ASRock Z68 Extreme4 is one example with the PCIe bridge chip.