They actually look very similar considering that these are two different graphs from different people who are bound to have somewhat different methodologies and equipment for testing. Driver variances are likely another reason for the slight differences. I assume you're trying to decide on the 250 ohm vs. 600 ohm based on which one has the stronger (or weaker) bass? My advice would be to buy the one that you can most adequately power as they will probably be quite similar in bass response.
That's right. I was looking for the strongest bass.
I appreciate your help.