Scrub potatoes and dice into ¾-inch (2 cm) pieces. Cook in large pot of salted water until tender. Drain well; let cool slightly.
Meanwhile, in a large bowl, mash eggs with a fork. Whisk in mayonnaise, whipping cream, sour cream, mustard, lemon juice, onions, and mint, until creamy. Add warm potatoes to dressing; season to taste with salt. Cover and refrigerate until serving.
To serve, in a medium bowl toss berries, arugula and balsamic vinegar; reserve some of the berries and arugula. Fold berry mixture into potato salad. Serve in a bowl or on a platter; garnish with reserved berries and arugula.