does pcie 2.0 support crossfire or sli?

Solution
Virtually no difference in lane speed.
https://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518/
Impact of PCI-E Speed on Gaming Performance

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The support is more of a function of the motherboard, most do but some do not. PCIe 2.0 is compatible with both as long as the motherboard can handle it. You would need to check the specs with the manufacturer.

As for a good GPU for the 9590, you can get yourself an R9 390X it would pair well.
 
SLI requires 8 PCIe lanes for each slot, but it doesn't actually require any specific PCIe revision. So even though a PCIe 3.0 x4 slot has the same effective bandwidth as a PCIe 2.0 x8 slot, only the latter would work for SLI.

Crossfire doesn't even have that x8 requirement.