well the yamaha dx7/dx1 "the famous/the big one"
actually its 12-Bit 6-operators
the DX7 II "mk2" its 16-bit 6-operators
the DX100 its 4-operators
Vintage Synth Explorer
the dx200 / plg150-dx are newer 24-bit
but still , natve instruments FM7 winns, becouse you can use a lynx l22 or rme hdsp9632, emu 1820m, or any other pro soundcard
http://audio.rightmark.org
comparison dx7 vs. dx7ii-fd (12-bit vs. 16-bit)
YAMAHA DX7 / DX7II: Sound Comparison
if you want the 12-bit sound, any decimator plugin will do the trick,
korg mde-x, basementarts. frantic filters, waldorf d-pole, free mda plugins
etc...