Oil changes and fuel milage

[janaka]

i thought that i'd post this as its something that I have been wondering and contemplating a bit lately as both cars in my household are used for a lot of driving (IE we drive in apprix 45000km a year per car).
I have heard that doing oil changes more often results in better fuel economy and wanted to hear what some people on here have to say about it. I own two honda's which according to factory specs need an oil change every 8000km. I know that when we go to Derek's (beverly tire on hespeler) his sticker reads next oil change in 5000km as its standard practice for a majority of cars (except for newer model years it seems).
I'm wondering if it is worth changing the oil in my cars sooner than the recommended 8000km to say even 6000km gain economy. I generally do al my own oil changes so it costs me about $50 for both cars (same oil filter and oil thankfully!) and a little bit of my time which I have no issue with.
Do you think that it will help to the extent of netting better milage?

Cars we drive
06 civic EX 1.8l 5spd- average fuel economy as calculated by hand is 6.1l/100 by my wife highway, 6.6l/100 by me mixture (town/back roads little to no highway)

04 accord EX 3.0l v6, 6spd- wife 7.4l/100 and i'm 9.6l/100 (same driving as above)

think there will be a noticable difference?