I usually do long interconnects and short speaker cables. I prefer to keep the driving impedance the speakers see low, more to terminate the crossover than for loss (which is usually negligible). Aside from controlling back-EMF, higher impedance from long speaker cables can change the frequency response of the speaker slightly -- how much depends very much upon the speaker, as well as amplifier and cables (cables are usually insignificant). That is also the reason I usually match speaker cable lengths, but in the real world that too is negligible (more me being anal) especially for short runs (10 m is fairly short).
For interconnects, I usually use XLRs for long runs and/or when the power amps are on a different circuit to deal with ground loops, but there are also lots of line-level ground isolation units available now (and few balanced-output consumer products). I have some ancient cheapie 50' RCA cables I have used many times that worked fine unless I was near a radio station or using them at some live venue and needed better shielding. The output impedance from line-level sources is much higher than from a power amp but still very low compared to an open circuit (antenna), usually 100 ohms or less at the driving end (admittedly much higher at the receiving end).
FWIWFM - Don