Mono amps and different length speaker cables

You won't hear any difference.
Don't sweat the small stuff.

If you believe that cable affects the sound then longer cable should affect it more, but your cable can be so transparent that 50% difference won't be audible. I still would not do it for the reason of resale value that Wolf_garcia mentioned.

I have tried it before & yes there is a audible difference. Whether you hear the difference I can't say.

Agreed with Mustang. You're talking 3 feet for signals traveling close to light speed.

Coaxial goes about 2/3 the speed of light, so that might be a factor :)

Not, as many have said, you can hear the difference but there is the ability to measure the resistance difference in cables, often of the same make, type and length. Whether that translates to 'hearing' difference is debatable as the amps performance can have a more substantial impact. Enjoy the music and stop fussing about the gear.