Put the potatoes in a large pot and cover in cold water. Season the water with salt. Bring to a boil, then gently boil until fork tender. Drain and cool. Break the potatoes up into chunks. You can remove some potato skins, if desired. Meanwhile, in a large bowl, stir together the mayo, mustard, lemon juice, pickle juice, pickles, red onion, scallions, parsley, dill, and cayenne. Season to taste with salt and pepper. Gently stir the potatoes into the mayo mixture. Fold in the hard boiled eggs, if using. Chill before serving. Garnish with parsley and dill.