PCIE X16

I have ZOTAC 590X , Soundblaster XFI Titanium, Bigfoot E2100 Network Card, and OCZ RevoDrive 3X2 240 GB. My question is, I have 2 X PCIE 16x slot and 2 X 8X slot. So when I use all of them, will my ZOTAC 590X work in PCIE X8 mode?

The revo drive is x4 I believe. Those devices besides the OCZ drive don't use much bandwidth. The network and sound card use x1. To answer the question unless you have another graphics card you are running at PCIe x16. Since your card has two GPU's then each GPU is sort of running at PCIe x8.