Speaker Cable Length

It's not about our opinions, it's about science. Plain old OFC is the best thing you can use. Refer here for gauge:

http://www.roger-russell.com/wire/wire.htm#wiretable

If it was me, place the amp between your speakers in the middle on an amp stand. Your 8’ cables should work then. If you are moving the rest of your equipment off to the side, you can run a longer pair of balanced interconnects to the amp. 
The rule was to use the shortest speaker cable as possible and run the longer length to the amp using balanced xlr’s. Having an amp low on the floor will not hurt the sq.

 No, IMO the heavier gauge would cancel any losses due to the longer cable.

@p05129 based on my center channel in the middle of my set up combined with the with the height of the amp I do not have room for both.  I’m all set with the XLR’s. My situation requires me to move my amp to the right side of my set up on the opposite side of my speakers and 8 feet is not long enough.  Appreciate your thoughts though. 

Another vote for shorter interconnects and longer speaker cable run, IF, one must be long. Whoever said the opposite must have been thinking backwards. Or use balanced XLR interconnects. Single ended interconnect signals are definitely more fragile than amplified speaker connections or balanced connections. 

Anyone claiming they hear a difference in speaker cable length is effectively stating they can detect something traveling at about the speed of light. Like, can you trace protons flying around the room?