For Demon House, I draw it at 8.5 by 11", at 300 dpi (always at 300, regardless of the project and reduced to 72 for web publishing). Then I save the pages for web at 650px by 841px because I've gotten used to seeing my pages at this size when I preview them in Finder. It's a little small, but it's too late to change the size I feel, with 12 episodes out already.
For my new series, I think I'll go a little bigger.