Metal Tart Molds - after they cool and are cool to the touch, mine pop out easily. Just turn upside down, may or may not have to give a little tap or slight squeeze.
IGI 4625 Pillar Wax is easy to work with and does really well with clamshells and tart molds, at least for the few I have made. Good h&c scent throw, I just hate that it's in slab form.
For sink holes, I've had that problem with that wax, I even mixed a batch with 20% 444 soy and still had sink holes. I have noticed that the larger in diameter the mold is, the less the sink hole is and seems like if I don't completely fill the cavities, like you show in your pics, then the sink holes weren't as noticeable either. I can do a 2nd pour but prefer not to.
Hope that helps.