You will find, IMO, that amongst the three primary Beyers dt770 is the exception to the 600ohm preference. I asked Headphile to build me a pair of Darths using the dt770/32ohm drivers (which I provided). When used with a tube/tubey amp - they easily superceeded the std Darths.
As it stands today, I have 2x X-Deeps, 1x 32ohm std Darths, and have arranged for Larry to transform a 2nd pair of stds to 32ohm. OTOH - I bought a pair of 600ohm dt990 when they first became available - still have them and they aren't leaving my desk.
What basically occurs is with the 32ohm drivers - the upper mids and treble brightens, ergo transforming the headphone to a more crisp, lifelike sound. But, some recordings make them too bright, which is why I suggest using a tube or tubey amp.. It all depends on your musical background and your personal listening habits. All of the 32ohm choices will experience the same phenomena. I don't think dt880 and dt990 profit from this option.......since for them the 600ohm option is superior to the std 250ohm....IMO