[II2II]

I ended up getting a faster Kobo! Thankfully, the slow load is a one time thing, per book. Depending upon when you tried it, KOReader has switched to a progressive model of updating it's caching (with most of it being handled in the background) when modifying a book's formatting.

That said, I think this may be mostly based upon a book's formatting. Messing around with upload options in Calibre may help. (For example, Calibre recently added an option to speed up load times with Kobo's reader software.)

[mkozlows]

That Calibre option isn't relevant -- it's for Kobo's native stuff, which treats "KEPUB" different from regular ePub, in ways that I haven't bothered to remember.