Speaker cable length

Going by what Gene says about cables is useless. None of the cable stuff matter to Gene. And a lot of other things.

another point of view

https://www.youtube.com/watch?v=WXPAjnmhK_g

J.Chip

I have exactly the setup that you are planning on. Keep the Left & Right the same length, it matters. That's just physics. Now people can argue they can't hear the difference but they are talking about their own hearing and not the laws of physics. Of course with that setup you are going to have on the one side a lot more cable to hide (or manage) than the other side.
For this reason alone opt for quality solid core cables that are easier to handle. Your ears will thank you as well with superior sound. Check out DNM's range and pick something you can afford. when looking at their products don't think that the cable's are specific for their amplifiers etc. That certainly true that they are designed in conjunction with everything else but they are tremendous in my setup.
Good luck with this.

Same length and not more than 10 ft after that the sound starts to degrade

Thus is controversial topic and I have heard all sorts of statements. What seems to be consistent at its base (I'm going to ignore brand names and technology to keep this less controversial) is that length of cable and Guage of cable matter. I dont have any hard numbers to contribute but for longer distances let's say 25ft the wire Guage should be higher ie 12AWG. I dont have a sense of low distance and what Guage you can get away with. Theoretically if its a 3ft run the Guage shouldn't matter that much. In audiophile land however I'm sure everything matters and so opinions will be hot on this.

 I keep it really simple and go with monoprice 12awg. I buy terminal plugs and make my own lengths. This might cost you $70-80 or less to make a 100ft run if you chose. Once you get into branding and technologies however the arguments explode. I do know people with monos will argue for shortest length possible as one of the advantages is to be able to place your monoblock right next to the speaker. Ultimately if someone is building a system it seems most prudent to spend the money on the best components and treat wire as the final thought to save up on if one so chose. Otherwise 12 awg from any brand with your own terminal plugs is great.