FPGA 060 @ 100-500MHz+ based, PCI, AGP(?), Not fussed about PCI-E, 512MB+ RAM, NIC, USB, RTG, WPA2 wireless,PCMCIA/PCARD in micro atx size would be me.
Maybe PowerPC... AmigaOS 4.. but can live without.
Don't even need a case, I'd sell my classic A1200 for that :-)