You probably chose that journal with a good reason (i.e. not at random). I know of many fantastic results in "non-top" journals (e.g. Szemerédi's theorem), so please don't worry. If your results are good, they will be recognized and used. Of course some strategy in life is useful, but personally I don't think it is a good strategy to delay publication and annoy several people (editors, referees) at the same time.