All mainstream pci-e 3.0 x16 video cards should run with pci-e 2.0 bandwidth with your motherboard.
With a CrossFireX dual card setup, both video cards would run with x8/x8 lanes using pci-e 2.0 bandwidth.
From the ASRocks online specs for your motherboard:
- 3 x PCI Express 2.0 x16 slots (PCIE2/PCIE4: single at x16 (PCIE2) / x8 (PCIE4), or dual at x8 (PCIE2) / x8 (PCIE4) ; PCIE5: x4 mode)
- 2 x PCI Express 2.0 x1 slots
- 2 x PCI slots
- Supports AMD Quad CrossFireX™, 3-Way CrossFireX™, CrossFireX™ and Dual Graphics
A single Nvidia card should work OK, but there is no mention of SLI support for a dual or 3-way SLI setup.
Check the motherboard manual for additional graphics details.
With my older P35 pci-e 1.x system, I get excellent graphics performance with my GTX 460 SLI pci-e 2.0 video cards.