When it comes to impressions I find mainstream places like Headfi used to lean towards the HD600 because of that typical Audiophile tuning while more serious communities prefer the more natural tone of the 650 with the extra resolution and detail. I actually find these days more people tend to prefer the 650. The 650 drivers are superior, it's a cleaner driver, faster, better controlled albeit it's newer driver. It's just preference really at the end of the day. The 600 has an upper mid peak and a bit more sparkle so in comparisons it can come off as a more fun listen because the 650 doesn't boost any of the response minus some warmth. I stopped doing comparisons like that because I always used to lean towards the more exciting headphone. Now I go by what makes me more engaged to the music and if the 600 does that for you maybe that one is for you.