Ah, yes, the format. That has impact too. I convert everything to .lrf, the handling on the device seems quicker (especially the 'formatting' part when you first open a book), and of course the margin and font size issues I see with rtf and pdf.
Dammit, I really want to tinker with my 505 but as I bought it in the USA and I live in NL, returning a bricked device poses an issue