RCA single-ended types are prone to noise pick-up whether from electromagnetic interference or from radio frequency interference and will have high frequency degradation once over 6 feet in length.
The reference to high frequency degradation for lengths longer than six feet is misleadingly oversimplified. The length beyond which high frequency degradation will occur is directly dependent on both the output impedance of the component driving the cable, and the capacitance per unit length of the particular cable. If both parameters are reasonably low, high frequency loss will not occur until the length becomes much longer than six feet. If you indicate the model number of the preamp, I can probably ascertain its output impedance, and provide some specific calculations.
These high frequency losses, btw, can occur with balanced as well as unbalanced interconnects, if the output impedance of the driving component is too high in relation to cable capacitance.
Emi/rfi problems, and also ground loop problems (which unbalanced interfaces can be susceptible to, and which can be sensitive to cable length), are dependent on unpredictable factors, but commonly do not occur in setups with considerably longer runs, and sometimes do occur with shorter runs.
The least signal degradation will be associated with speaker cables since these are carrying a higher power signal where effects of resistance, capacitance and inductance are easily overcome with the stronger signal.
This is simply wrong, and reflects a lack of understanding of both the amplifier/speaker interface and line-level interfaces between electronic components. Resistance, capacitance, and inductance are not "overcome" by signal strength. They have effects that may or may not be significant depending, among other things, on the impedance characteristics of the components that the cable is connecting.
Under most circumstances, capacitance is not a significant factor for speaker cables. Resistance and inductance can be significant, depending on the impedance characteristics of the speaker (including the manner in which impedance varies as a function of frequency), the damping factor and output impedance of the amplifier, how sensitive the particular speaker design is to damping factor and amplifier output impedance, and other factors.
Under nearly all circumstances, resistance and inductance are not significant factors for interconnect cables, while capacitance can be, as explained above. Signal strength has nothing to do with any of that; it is a matter of the relation between those parameters and the input and output impedances of the components.
Please do read the thread I linked to in my earlier post.