I think I'm making some good progress there. The next release should startup faster. But 7 seconds on the N8x0? Not even microB achieves this (just measured; 9 seconds).
As weird as it sounds, it's a full screen rendering because of changing the layout and the toolbar contents. I'm now trying to minimize the amount of rendering a bit further. Especially the toolbar stuff should be optimizable.
The screens contents are moved by the amount that you scroll (Xserver-side pixmap copying). Only the newly visible items get rendered. Every time a new item with a thumbnail gets rendered, the thumbnail has to be read from file. There is some thumbnail and item caching involved, too, for speeding up the process, but these caches can't hold many items.
Text rendering can take some time when pango has to lookup new characters (e.g. for displaying CJK characters), but once the characters are loaded the delay won't happen again.
It would be interesting to see what happens when you disable thumbnail loading and rendering by opening /usr/lib/mediabox/components/media_viewer/MediaItem.py and commenting out the line with