My opinion at this stage is that QupZilla is very promising but not quite ready for prime time. It's certainly fast, and I haven't experienced any significant rendering problems, but the issue which has made me put it aside for the moment is that I can't organise bookmarks in the way I want because the editing capability is very limited. The other small oddity is that a pointless scrollbar appears to the left of some forum messages when avatars are displayed - unimportant but slightly distracting.
I'll give some feedback to the developers, and I'll keep an eye on its progress, but for the moment I'll be sticking with Firefox.