Hey Murf. I can't find any justification to move away from the DR-680MK2 and remain totally content with it except when I wish for more than 6 analog inputs. Menu system of the MK2 is much improved making it easier and faster to navigate than the older MK1 version. Can pretty much use any decent SD card. Not as small as some of the more recent options, but a strong value point. I really like my old OCM R44 but rarely use it much any more because I pretty much always use the DR-680MK2.
The 680's primary feature for which I can't find an equivalent in any other deck is the super-easy channel linking, which lets one adjust the gain of all recorded channels simultaneously using a single knob. That feature alone makes it worthwhile. Yes SD can link 4 channels on a few of their machines, but AFAIK cannot do so rapidly and easily with just two button presses. So if you need to un-link to tweak just one channel then re-link them all for single-knob level adjustment, doing so is easy and straight forward.
It also has digital in/out if that's important to you.
It's weakest feature is the metering, which is not detailed but is sufficient to get the job done with good recorded levels, so it doesn't bother me much. I imagine it would bug others though.