What is the longest RCA IC (my friend) can run?
It's highly dependent on the capacitance of the cable and the output impedance of your source component. Both should be as low as possible for a long run, or else the upper treble will be attenuated.
Also, the shield quality needs to be as good as possible, in terms of having low shield impedance, and providing effective shielding. That can be hard to assess, though, other than by trial-and-error. Hum and/or noise would result if those factors were inadequate.
See the following thread for some specific recommendations, including the Blue Jeans that were mentioned above:
http://forum.audiogon.com/cgi-bin/fr.pl?fcabl&1229395958
Regards,
-- Al