sn8kbyte,
I know that my server handled my max traffic day like a breeze. I have the ds2 plan from m3server.com though.
Was a pretty fair chunk of folks as well
Beyond that I'd suggest checking around at the wordpress support forum:
http://wordpress.org/support/
and I'd love to hear what you find out by posting there.
I would imagine that wordpress would do fairly well at higher volumes (6 figure uniques)