If you have poorly designed speaker cables that are of a high nominal impedance, you may make gains by going to long runs of balanced interconnects and keeping the speaker cable short. Otherwise, i would suggest using short interconnects and long speaker cable or a combo that is a median point.
Just bare in mind that long interconnects typically have little to no resale value where the opposite is true of speaker cables. I have purchased 20+ foot pairs of interconnects for amounts equal to or less than a standard 1 meter pair would cost. I was able to do this because the seller could not give them away. Having done that, i cut them to the lengths i needed and re-terminated, making out like a bandit. In some cases, i was actually able to sell the left-over cabling that i did not need for what i paid for the whole lot. Sean