Do you have any idea how they would compare with HD-600 or HD-650 for example?

So beautiful...You could compare with other phones of same price range .-.

I have owned a pair of HD600 and have listened to several HD650. They are closer to the HD600 in sound is it is the more balanced of the two headphones asked. But the SRH-1840 is better than both in my opinion as it has a better defined bass, more present mids, and in my opinion more realistic sounding treble especially for instruments like cymbals and drum kits. I would say the 1840 is up to the quality of the Beyerdynamic T1 but is not quite up to the quality of the HD800. But it requires only a modest amp and is cheaper than many $1000 headphones so is a good value in my opinion. I also like this headphone better than the AD900 I used to own.