Noir what basicly happens is this. As the weight and wing loading goes up you have to go faster to create enough lift to fly. Thus your take off speed rises as does your landing speed. Highly loaded planes do not hande as well. They take longer to turn and so on. As several of the posters have mentioned as the size of the model increases. So does the ability to carry heavyer wing loadings. I hope this simplifies this for you.

Mark Shuman