CSSU comes with Qt 4.7.4 so I dont have concerns on Qt side. Though I think QML on Harmattan is newer that the one on Fremantle, that is why I asked to keep it compatible, if it is possible. SW rendering (esp when gcc 4.7.2, thumb compiled) is pretty fast, at least it was in my Fennec 17 builds. Waiting the current build to finish(it takes eons in scratchbox), will see what is the situation.