The quality not the quantity of work affects the assessment outcome. 200-350 words across both tasks if aiming at grades D-G, 400-600 if aiming at grades A*- C, is for guidance only. Obviously, the shorter the assignment, the more difficult it becomes to meet the upper bands of assessment criteria for CONTENT (and therefore other categories). There is no upper limit on the number of words. The whole piece will be read and marked by the examiner.
There is no limit, trust me, for my GCSE German, Spanish and French I wrote the near minimum amount and still got A*'s. In GCSE it is more about the quality and how `complex' your writing is rather than quantity.