Don't bother unless you are biamping. You just don't get enough out of it, if anything, to make any significant difference. If you think you can hear the difference in speaker wires, just get thicker ones. At least they'll be phase coherent.
O course if you want to experiment and use different lengths like 20 foot and 150 foot for high and low and see if it sounds different, go right ahead. In fact post the results. They probably won't be all that good as extra wire is no good. Not that I say cut it so you can't even vacuum behind the speakers, but withing reason and taking into consideration the possibility of setting the system up in a different configuration, or room.
If you have two amps, put the one with more power on the low end. If you do not have an active crossover then just turn the bass down on the amp feeding the high end. This is the minimum setup that is universally recognized as being better. However don't go overboard with the amp discrepancy. Depending on the crossover, you want the treble amp to be at least half the power of the bass amp. It does you no good to use a 300 WPC amp for the bass and a 10 WPC for the treble.