Lets not rate wire by car audio amp wattage. Since 9/10 times this 1200W amp turns out to be a Pyramid amp. Lets ask factual questions like the amps fuse rating or current draw (in amps).
If your amp has a 40A fuse, its really a 500 watt amp unless they have created the world's first 100%+ efficient amp at 12-14V
Over 50A @20ft would require 4AWG. Length is VERY important, 50A at 2ft 10AWG could support that load.
Also with the V x A equation, that also figures the amp to be 100% efficient, which they are not. Its a good rule of thumb though.
95 Contour SE '01 3L 
