I can't give you any hard data on how big a map is too big; that's something you'll have to gauge for yourself. For my two cents, giant views aren't often desirable; zooming in on a smaller view will tend to look nicer. Larger views will impact server performance, though not as much as they once did.

The DSified webclient is out now. Everyone using the webclient (or those considering it who haven't yet), please test it out and report in Beta Bugs.