I've upgraded core MT router from 3.xx to 4.3. We keep Queue List running in winbox at office to monitor simple queues, as well as Interface traffic graphs.
Since upgrading, the Queue List will virtually die after a few hours. If you double-click on an entry, it will refresh it's line, but the rest of the screen remains unchanged.
There is a couple hundred Simple Queues, and it's running on a AMD Athlon x2 box.