The primary difference was in headroom...I would call it meaningful. Night and day, no, but not imagined for sure. At levels where the 6200 sounded as if it was out of steam, the 8300 still sounded clear. Since my room was considerably larger than my previous one the 6200 was getting "lost"; I needed more power to fill it adequately. When I went to 4 Ohm speakers, I neede to add the monos because the 8300 wasn't able to handle it too well.
When people say you need to double power to achieve +3dB, we are actually talking about a 50% increase in SPL, so it is quite noticeable. +1dB is easily heard by the average person - if you don't believe that, try adjusting one of your speakers up or down in your speaker config by 1dB and then tell me you don't hear it - this is why calibration is critical.