I have a 02 Accord EX, and also extend my OCI. I however run off the shelf synthetics when doing so, and at one time was shooting for 15k OCI, however to be honest I hot around 13K before I change when using a synthetic. I also use a top tier oil filter.. but I'm not sure this is really needed to the point of my 13k OCI..
I also run conventional, and this is my best bang for buck OCI, I get 10K on conventional using a top tier oil filter and the oil filter of choice of last few OCI's have been Fram XG.. and when using conventional I run the oil filter for two consecutive OCI's.. I know many scuff at this regimen, however it is noted in the Honda owners manual as to running the oil filter for two consecutive OCI's, and I'm also running a top tier filter in which I think the fram XG is a much better built filter than the OEM... I have also used lesser grade filters with no problems.. and I will also admit that I do not hit 10K every time, sometimes 8k but always between 8k-10k.
So in thinking about this in a scientific way, we have no problems running a filter for 15-20k using top tier filters, so it should be perfectly acceptable to do the same thing when running conventional, not because your a cheapskate, but because the filter can handle it, the OEM recommends this practice, filters may become more efficient when doing this etc etc.. Also your looking at a very very low cost oil maintenance regimen using top tier products,and the most important of all is running what Honda specified in oil type/grade/etc (LOL)
BUT this is not a jab against amsoil by no means and I will make a point that M1 5w-20 EP is in my sump at his very moment because of the good deal I got, it seems I run synthetics more than conventional... I'm lazy and put on a lot of miles so using synthetic get me a few more thousand miles without having to fool with oil changes, and this is perfect when the weather is freezing cold/wet or hot/humid.