I'd suggest it's probably most effective playing against opponents roughly one to two hundred points higher than yourself.
As the saying goes,, 'A man's reach should exceed his grasp.'
Within this range you'll obviously lose more often than you win, but you should get enough close games in which you can hopefully see how your opponent is slowly but surely gaining the advantage; playing chess at the next level up, which is where you want to be.
>200 points though, and probably all you'll learn is how you'll be punished mercilessly, the first mistake you make. That's my experience anyway. 🙂