Throughput or bandwidth? USB 3.0 operates at 4.8 Gb/s (bandwidth) where current SSD's use SATA 3 Gb/s (bandwidth). Throughput, however, depends on the medium; SSD's using the same SATA 3Gb/s interface as mechanical (legacy) HDD's perform faster because of the way the medium is implemented (platter vs. flash), despite the interface having the same bandwidth.
As for the speed of USB 3.0 devices, we won't know until they are released.