If you want a Roland/edirol I would get an R44 instead of the R4!! Newer model, smaller, and doesn't resample the digi in.
but not available in the YS currently which as the original criteria (although I do agree with you, I'd get the R-44 first).
Mostly local bands in bars but also jambands. I have a couple of WSP shows coming up. My mics are Nak cm300, CA 14s , At943 Hypers, and adk sc-t. My pres are ca-9200, UA5, Niant big box and a DV promix 3. I would not need more than 4 channels very often and power would either be alkaline batteries or I also have a naztech 1500 and wouldn't be against getting another or dvd battery. Remote power is not really a concern I can get whatever I need. To me it is mostly a question of how much do I want to spend on a recorder. A modded r4 is pretty much my dream but the tascam is less money and an upgrade from what I currently have (dr2d and pmd670).
Ok, well, two things that I'd read up on and see which bothers you less for your environment:
The R4 is bigger, and uses an hdd (and CF mods have so far proven unsuccessful). There is something in the design that will cause the hdd to produce write errors under heavy bass (e.g. electronic/dance levels of bass) so lots of care is needed to ensure vibration reduction padding is adequate. Second, if you use the digital in, you only get 2 channels, you can't do a mix of 2+2 with the digital connection. The downsides of the 680 are that a number of people have fried theirs when field powering them, they seem particularly finicky about that. Second, it seems to occasionally eat a file so you come home with nothing. If you need the extra channels on the cheap, it's an ok recorder, but it's not something I'd put myself in a position where I had to have a recording at the end of the night. Lots of people love them and have no issues, so read up through the unit's thread for detailed info there.
//disclaimer; a guy I know used an R4 when I was taping with him a lot so I have more first hand knowledge of that unit and the threads here on TS. I have read the threads on the 680, but I haven't run one nor do I have any extensive experience in the field taping with others who have.