Asus moved the Sabertooth 990FX GEN3 R2.0 into the limited production status and have seen prices nearing $255.00 Usd for one when available.
Because there is nO PCIE 3.0 support for AMD chipsets Asus had done some trickery. Actually a grand total of zero AMD PCIE 3.0 boards.. The Asus SaberTooth uses a PLX PEX 8747 splitter to double the bandwidth the PCI-E 2.0 lanes to approximate the PCI-E 3.0 specification, but the PLX chip can't do anything about the changing the encoding from 8b/10b (2.0 spec) to 128b/130b (3.0 spec - pdf), and of course, as with P68/Z68/Z77/Z87 boards equipped with the same bridge chip, you're introducing latency into the system by routing through it. Anandtech has an article that includes information on how the bridge chip actually works.
So price and actual experience of some forum users and the lack of need for PCIE 3.0 for most people, I would not be looking for the Sabertooth 990FX GEN3 R2.0 mobo.
RGone...