So, I've pretty much decided on Cygolite's Expilion. I like the ability to swap batteries easily and while none of this stuff is cheap, i think Cygo actually does a fair job of keeping prices midstream.
Cygo uses the same exact pic for light output on the 680 and 720. However, the 850 is *barely* brighter.....at least in the pic. The only thing I can assume is the lumen reading is still significantly improved.
The 680's (and 720's for that matter) claimed output pic ----> http://www.cygolite.com/images/expilion3/2bnew.jpg
The 850's output pic ------> http://www.cygolite.com/images/expilion3/2new.jpg
I'll spend a few extra bucks if the 850's that much better but if not, I think at $80 the 680 makes a good argument since they're otherwise the same friggin' light???