There's absolutely no way of predicting how much stretch in your ears would make the enlarged holes permanent. Each person and their skin varies too much. I started stretching some of my ear piercings almost 20 years ago and each ear has a series of 2g, 4g and 6g rings in them. They still start to tighten up when I take the jewelry out for even one day, but most of the people I know who've done the same thing find that their piercings stay the same size when they take out jewelry for a while. I've known people who had huge tunnels (1"), took them out after a few years and the holes just stayed there like big loops, but I've also met a few who had piercings of a similar size and they shrunk back down to pencil-size.
Note that the different cultures who practiced ear stretching historically NEVER did this to be temporary. It wasn't done as a fashion, it was done as a widespread cultural practice. It was always done with the intention that the piercings would be large for the rest of the wearer's life, and often was part of the rituals connected to passing from childhood to adulthood.
I always say, if anyone ever had any doubts or hesitations about body art, it means you're not supposed to do it. This is one of those cases where you have to think what's right for you, and think ahead to the rest of your life in those considerations. If you stretch your ear piercings, you might find the change has become permanent or it might not. One more thing you should know is that ear tissue is a bit different from the rest of the body, and if you tear an ear piercing, or stretch an ear loop so that it breaks, the ear will never heal together again unless you have plastic surgery to forcibly rejoin the tissues.
To learn more about ear piercing, you can read more about every kind of ear piercing or you might like Body Piercing: A Medical Dictionary, Bibliography, And Annotated Research Guide To Internet References by Icon Health Publications.