Of course I suppose there can be variations in 75ohm interface quality too. For instance, my friend Larry thinks coax is best, but ONLY if it employs BNC (bayonet) connectors (as opposed to RCA connectors.)
That would be highly system dependent, as it would be dependent on the jitter reduction capabilities of the dac (if any), the risetime and falltime of the output signal from the transport or other digital source, the degree of impedance mismatch between cable, connectors, and interface circuits at both ends, and the length of the cable (which affects the timing of reflections and re-reflections caused by impedance mismatch; 1.5 meters is generally considered optimal, shorter than that non-optimal).
See this paper: http://www.positive-feedback.com/Issue14/spdif.htm
And this and other threads here at Audiogon: http://forum.audiogon.com/cgi-bin/fr.pl?ddgtl&1237611683
Given these kinds of system dependencies, and others which most likely exist in the case of optical connections, I think it stands to reason that experiences and opinions will differ on the op's question.
Regards,
-- Al