Assuming all else being equal, how significant is the difference in speed of rooting between a cutting taken now and rooted immediately vs one that was taken a week earlier and now just being rooted vs one that was taken one month earlier and now just being rooted? Assuming earlier cuttings have been well kept too.

i don't know how much of an issue a week will cause. but i know for sure fresh cuttings will have better results. UCD cuttings always roots easy for me. most of trade i have and all the generous cuttings i received are very fresh cuttings and i do not have any issue rooting them. all the failures are my fault only. 

typically, i cut my cuttings day before shipping off so it will be as fresh as possible. 

Fresher is definitely better. Cuttings taken from a growing tree root almost immediately for me. While cuttings taken from a dormant tree that are refrigerated for a time will have a lower chance of rooting. The fresher a cutting the better.

Yes, I think generally we can agree that fresher is better.  We can also agree that if stored properly, they can still root many months down the road.  I just want to know the signficant differences. If there is some kind of a table (fictitious below) for dummy would be good.

All else being equal,

Freshly taken cutting - 100% ease of rooting.
1 week old cutting - 90% ease of rooting.
2 week old cutting - 80% ease of rooting.
4 week old cutting - 70% ease of rooting
8 week old cutting - 50% ease of rooting
12 week old cutting - 25% ease of rooting
etc

At the moment, I have a batch of cuttings.  I am thinking of not putting all eggs into one basket.  I would like to root half first and see how they go and should I fail, I can try other methods or improve my rooting techniques.  However, I want to know the trade-offs of putting them away in the fridge until say 1 month or even 2-3 months later.  Will that make rooting even harder for someone who I must admit am a habitual rooting failure. :o

OK, another question.  What is the best way of storing in the fridge?  I have now wrapped them in newspaper, about 4-5 pieces thick and then put two plastic bags over them and into the bottom of the vege compartment.  Is this good?

I would have thought that fresher cutting would be easier and faster to root too. So I found it interesting that it turned out to be the other way lately. I have about 30 cuttings of a few varieties kept in my refrigerator since last November. I started rooting them a little over a month ago, along with many desert king cuttings fresh from my own tree. I was using the same method with the same rooting medium. Much to my surprise, the old cuttings, which have been kept for more than 4 months, in general have much more roots than the fresh cuttings. Many of the my old cuttings have graduated to 1-gallon pots. Of course, other factors, such as variety, may come to play, but desert king has always been easy for me to root. So the fact that these old cuttings root easier than desert king says a lot. At least, it shows that a properly kept cutting wouldn't make much difference in the rooting success.

I wax-sealed both ends, folded cuttings in food film, then put them in a ziplock bag.

Experiments have been performed. One that I  found was "Rooting Experiment".

From my observations this fall and winter after reading the above Topic, dormant cuttings have had a higher and faster rooting rate after being refrigerated (exposed to cold) for 3-4 weeks. I had several different varieties of collected cuttings which were harvested at the same time and sample viability tests were done. After refrigeration (3-4 weeks) the cuttings rooted at a greater / faster rate. The cutting ends were also sealed with wax, but were loosely stored in gallon ziplock bags with about 1/4 cup of shredded long fiber sphagnum moss per bag (30 plus cuttings per bag).

Wow, will and pete, thanks. I wouldn't have known this. This is such useful info.