Quote Originally Posted by bnilsson View Post
Will I gain much performance if I change to QWidget?
You'll lose the overhead caused by everything that QGraphicsView has and QWidget has not.

I suspect I would never get it working for a 150Mb data file if I use QGraphicsItems with QGraphicsScene/QGraphicsView.
I'm not so sure. One graphics item takes about 50 bytes of memory on average. How many items would you have in a 150MB file? 1M? That's less than 100MB of RAM used for the items.

BTW, I am using QDataStream to repeatedly read my data, even for updates. I guess this is not terribly efficient. Can you recommend another way?
Hard to say without knowing what your data represents. But if you do that constantly then that is surely inefficient.