@n80 ,
Differing lengths will have slight impedance differences -probably not that much but it can affect the sound balance/quality. It also might affect the amplifier.
I forgot the right side would have all the extra cabling, not the one under the floor. You could just drill another hole or two and put the extra cable under the floor in order to hide it, or just casually drape it somewhere unnoticed.
I would tend to agree with the other posters that you probably won't hear a great difference, but why take chances? If I did try two unequal lengths, I would have a backup plan in case it didn't work out- Like budgeting for another set of cables. Something like AQ GO-4's which are relatively inexpensive (and will probably be an upgrade).
A lot of this is system dependent, so what might work for one guy might not work on another guy's system.
B