The length of a speaker cable run does not impact delay. What is important is that the cable be sized appropriately for the power anticipated at the speaker and for the length of the run. The longer the run the greater the diameter the wire needs to be. For a 40 foot speaker cable I'd recommend at least 14 gauge speaker wire or 12 gauge (gauge is inverse of wire diameter) if your speaker terminals can handle that size. While there is much debate over the effect of wires on the sound of the speaker IMO a good quality wire of the appropriate gauge is more than sufficient. In my case, I'm using 14ga in-wall wire from Cables To Go with maximum runs to my surrounds of about 30 feet. I have 4ohm speakers and a 300w/channel amp and the speakers sound fine.