I've used qupzilla in the past (not this version) and the only thing that stood out was that it "felt" snappier.
Other than that I remember frequent crashes (however it was quite a while when I tried it, could be different now).
If firefox is OK with size and functionality, what about firefox-aurora:
http://www.phoronix.com/scan.php?page=news_item&px=MTU5NjM
Haven't found information though if it's based on the gtk3 version of firefox:
http://www.phoronix.com/scan.php?px=MTU2OTk&page=news_item
Using firefox-aurora right now and I like the interface.
Whatever we will use in the future, please take the web browser out of extra and give it his own sb file.
Happy testing