If the panels are wider than tall, 800 should be ok. But if they're square or taller than wide, I would size it down to perhaps even 650 px wide, so long as the text is still legible. I think the ideal should be, if you're on a standard monitor, to see at least the better part of 2 panels starting at the top of the episode. Because I hate it when one panel takes up the entire screen and there's no reason for it and then it's just a bunch of scrolling for the reader. Um, let me know if I need to explain myself better. lol