Another point to consider is the pilot. Two pilots ready to move on to the next step may require two completely different models. Reaction time, grasp of fundimentals, aggressiveness, and current ability to name a few, will dictate what would be a good next plane. The best way to make a decision is with the help of your peers, the ones whom you fly with regularly. As far as the difference in performance between low and high performance sport models, it is generally the the amount of R&D done to find the right balance of airfoil/airfoils, tail moment, thrust line, wing loading, etc. The best thing anyone could do is discuss what types of attributes they are looking for in a next model with an experienced modeler with whom they fly, list those attributes and request experienced pilots to respond with possible matches from thier experiences. This may give you a somewhat smaller list to pick from. In the end it is still somewhat of a guessing game.