SuperNoSpread is even more accurate that NoSpread considering that NoSpread isn't ALWAYS 100% accurate, it can be off by the slightest bit. I also believe that its bullet speed is improved a bit so that it hits wherever it was shot by the time that the gunshot stops playing, AKA click and it appears instantly wherever you shot.
I believe that the above is true, but I can't be 100% sure. Just my perspective.