I haven't tried the 880, but I have tried the Performance 840 and the Pro 900i back to back. The 840 sound signature was much less V-shaped than the 900i. (This was with only 20 hours or so of break in.) Actually, the new-ish 840 was in between my well-worn HFI-580s and the new-ish 900i in a lot of ways: It was more comfortable than the 580, but not as comfortable as the 900i. The sound quality was more refined than the 580, but not as refined as the 900i. The sound signature was more bass-heavy than the 580, but not as bass-heavy as the 900i.
Obviously, the 840 is different than the 880, but hopefully this will give you some point of reference.
P.S. I found the DT770 almost unlistenable, but I have a high-mid sensitivity right where they have a spike.