I have seen people suggest before that you look at the difference in stitch numbers between sizes, such as substract the medium stitches from the large stitches and then add that to the large size stitches.
Yes, that works well. Another way is to use larger needles. Figure out how many sts/inch you get with the bigger ones, how many inches you need and multiply those numbers. If the number you get is close to one of the other sizes, use that size for your pattern.