Aging HD590 vs. new ATH-AD700?

I had packed my HD590s away years ago in the mistaken recollection that they were broken, only to realize that they're still working fine -- I just need to buy new earpads for them. I'd been thinking about buying the ATH-AD700 as a replacement open-backed phone because it goes for pretty cheap now (I don't think I can afford the AD900), or I could save about 50-60 bucks by shelling out about $30 for 590 pads. But I also have to consider that the HD590s are about 7 years old now, and were reconditioned when I bought them so God knows how old they really are, so it's possible that I would buy new pads just to have the thing die of old age soon anyway, especially since it's been sitting around with no foam covering on the inner driver assembly to protect the diaphragms from dust or whatever else you're supposed to protect diaphragms from....

I like the sound of the HD590, but if the AD700 sounds substantially "different-yet-similar" to the HD590, I might be tempted to shell out for them and then fix the 590 pads later. Has anyone here ever done a detailed comparison of these models? (Soundstage, sonic signature, balance, detail, ease of driving, etc)

All comments/advice gratefully accepted.

P.S. I read the thread announcing that Audiotechnica is releasing a new line of "ART" phones, which will almost certainly include replacements for the ADxxx series after they roll out their closed equivalents. Do you think this will result in a price drop on the older models, or will the older models gain an extra halo of specialness because they represent the last of the famous "winged" headband design?

I'm not really sure how closely the HD590s resemble the "house" Sennheiser sound, since I've never had the opportunity to try the HD595, HD600 etc. The HD590s were considered a relatively bright-sounding anomaly, if I recall from reviews, leading some Senn lovers to bash on them.  A lot of their complaints -- recessed mids, grainy treble, etc -- have also been applied to some members of the Audiotechnica family, which makes this choice a bit of a puzzler for me.

I'm OK with the Audiotechnica fit. I owned the A900s once and they sat on my head OK until one of the "arms" that holds the earpiece onto the headband broke, making everything kind of weird. And a relatively loose fit on an open-backed headphone is less of a problem that it would be on a headphone meant to isolate sound....