I would imagine Gravity is a natively compiled C app for a start. Witter is python which is always going to be slower.
The problem isn't really a question of *how* to write the code, more a question of how much code it is to write.
I'm certainly not about to spend hours and hours coding up avatar support, just to find it drags the performance to unacceptable levels. There is no point investing that time until I can make the current capabilities work with smooth scrolling.
Anyone that has any ideas how to get faster performance out of python, I'd love to hear them. Currently I'm using GTK, a hildon.pannableArea with a gtkTreeView in it. It doesn't seem to matter whether I use my custom cell renderer or the default text one, neither runs particularly smoothly.
I don't have any real idea how to find out what is the performance issue, I'm assuming that the above combination is just not that fast, but maybe I've made mistakes elsewhere which are costing. Don't really know how to proceed.