Sorry to be picking a nit here but the SwinSID is not FPGA based, it's a software emulator running on an AVR mcu.
There is an FPGA based version of the SID called (surprise) FGPASID (http://www.fpgasid.de/) which is pretty much indistinguishable from an original SID. The only real downside to it is the cost, it's not a cheap one.
The FPGASID was created by decapping and reverse engineering original SID chips and the result is pretty spectacular.