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.
And, it emulates two SID chips and has multiple modes (6581 and 8580), so it seems like a pretty darned good deal, honestly.
Real SIDs are pretty pricey these days, and they aren't making any more of them, so they will keep climbing in price for as long as people find them interesting. So, it's good to have an alternative.
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.