Long wire PWMed LED lights
Wire capacitance at such current is negligibly small. Don't worry about this at all. 

According to wikipedia - typical AWG 20 wire resistance is 33.31ohm/km. 

With 8m distance current travels 16m of conductor total (there are 2 lines/cores in wire). 
0,016km * 33 ohm = about 0,5ohm
At 1A current you will loose 
U=I*R = 1*0,5 = 0,5V

Maybe use a bit thicker wire to reduce voltage/power losses?
Additionally - resistance differences will dim your "far leds" more than "closer leds".

Long unshielded wires with few Amperes PWM signal will emit some EM indeed, and you may hear it in your audio equipment. To aviod that you may put transistors at leds, and use 2 wires - one coaxial for just PWM signal and AWG for power. At the end of power wire and before transistor put electrolytic capacitor to reduce EMC noise emitted by power wire. Like this (thats just idea visualisation):



You have very small inductance there, you don't need flyback diode.

Sorry if I did some language mistakes, my english is not perfect.