I'll second the fact that that cel is 
incredible!  I don't even collect CCS.  :)

As for resolution, mine varies anywhere between 
800 X 600 to 1280 X 1024, depending on what I'm 
doing, and at my current resolution (1280 X 960), 
that thumbnail is smaller than my thumb, and I 
have small hands.  IMHO, I think 40 to 50 percent 
bigger would be good to be able to make out more 
of the cel, yet still small enough to be quick 
loading.  On my site, all my thumbnails are right 
next to each other, so I like to keep the cels in 
proportion to each other, even my 2.5 foot 
Tamahome pan.  :P

~the red hood