To be honest, I tend to use medium as a direct replacement for large, i.e. use 2 where it says 2.
In savoury things I doubt it would make much significant difference. Possibly a slight difference in baking.
If it's a basic sponge you can always weigh the eggs and use the same quantity of four / butter / sugar e.g. if it says 2 eggs, 4oz flour, 4oz sugar etc. then weigh your medium eggs, and whatever they weigh, use the same quantity of the other ingredients so it's all in proportion.