How large should comic art be?

When I'm making my webcomics I'm doing it in a printable layout, 3750x5625/300dpi (Bleed included). The page itself is 3576x5501/300dpi and the panels are between this square, on a 3222x4841/300dpi territory.

When I'm done, I'm reducing it to 600x900/300dpi (My personal webcomics panel standard).

Here is a template. It has almost the very same layout what I wrote above.
http://fear-is-spreading.deviantart.com/art/Comic-Page-Template-122355305

All your panels will be a huge file, so be prepared for it on your hard drive (A Disk Defragment is also advised on your drives and partitions before you start it as loading and saving very large Photoshop files is requiring a bit more work for your hard drive. Disk Defragment is also expanding your hard drive's life time under these operations.).

There are no general rules, especially now that comics are in all shapes and sizes, but if you want to print them eventually, it's good to go for common comic book size. It's around 6.625x10.05 inches for American pocket book, or A4 (21x29.5cm) for the rest of the world. You can work on a bigger size of the same aspect ratio. In photoshop make sure your pages are in either 300 or 600dpi. I work on 600dpi myself; the bigger the better.

I just think you need to stick with high resolution. anything over 300 will work, but 600 would be ideal. As far as size, generally I'd say it should be at minimum, the size of the page you're trying to print it on, but should be larger.