Mirabels (cherry plum) grow huge though, far too big and chunky for a container, surely, too big even for the pinch bar hole. Also the blossom, whilst early, is very unimpressive. They take a few years to start fruiting, then you get your first 'miracle' when you spot your tree covered with ripe fruit. I love mirabels but in a different situation to Karen's.
The pink hawthorn could be a good idea - they make a nicely shaped tree when grown away from a hedgerow.