@leftylucy - right now there is only a high-score monthly challenge. We're looking into ways of possibly adding fastest solver competitions in the future, broken down by puzzle size.
Each subsequently larger puzzle size has an equivalently larger maximum score assigned to it. The 4x7 puzzles are the largest and have the highest maximum score.
@chagler - there is no 6x7 grid, leftylucy was referring to our 4x6 and 4x7 puzzles.