Btw, anyone seen a non-BGA S-ATA to LVTTL/LVDS bridgechip or similar that can interface to an Xilinx Spartan FPGA ..? S-ATA = 1500 Mbit/s ; USB2 = 480 Mbit/s
You mean one of these? This board has two Samsung SATA 3G PHY's (i.e. 3000 Mbit/s too)

They are just PHY so you need your own SATA controller to program into the FPGA.
Choose a newer FPGA and you can use the RocketIO to pretend to be a SATA PHY (i.e. no extra SATA chip)
Economically though, you'd be much better off looking for a microcontroller ASIC which has both of these functions and some sort of DMA capable I/O. There are 10's of them out there.