Those are pretty good hotel choices on the whole, though I'm not a big fan of the 4 Seasons. FYI, at least the 4 of those properties at which I've stayed/booked (Beijing, Hangzhou, Xian, and Shanghai) have been known to cough up pretty nice discounts when pressed. Weather shouldn't be a problem.
Try posting in the "Asia" forum; you might get more action.
PS - If I were you, I'd trim Xian and Hangzhou down to one day each (and maybe even reduce Shanghai to 2 days) in order to spend more time in Beijing.
[This message has been edited by moondog (edited Feb 19, 2004).]