The only downside of using larger wire is shorts/bursts which can get dangerous fast, so make sure you fuse it properly and you'll have no problems.
The upsides are well worth it. You want your amp to easily be able to draw current, so use the largest wire that your amp's terminal can properly fit (properly means the wire fits in the terminal with no cutting/trimming/twisting, etc). But for a 560 watt amp, 4awg is plenty. 2awg is overkill and will net you nothing until you step up to a larger system with multiple amplifiers.
Last edited by mSaLL150; 01-05-2010 at 02:23 AM.