Pciexpress16x vs pciexpress 2.0

PCI-Express is a standard, and the number (2.0 in this case) means the revision of the standard.

There are PCI-E 1.1 x16 slots and PCI-E 2.0 x16 slots. PCI-E 2.0 offers twice as much bandwidth than PCI-E 1.1.

A PCI-E 2.0 x16 card will work in a PCI-E 2.0 x16 slot, and in PCI-E 1.1 slots as well.