Raijintech Morpheus II aftermarket air cooler - works with Vega's, though not designed for them.
Advantages are: good temps and damn near silent and it may end up with you applying better thermal grease, which should help whether you run Cast or something else.
Cons: sets you back $60, somewhat delicate operation, exposes back side of the Vega
Disclosure: temps no better than setting stock blower fan to 3,000/3,500 rpm -- but the Raijintech Morpheus II + 120mm fans is silent by comparison.
Start here for an overview:
https://youtu.be/THaMlkNDzYsThe YouTube video leaves out a few steps. Here is what I would add:
1. Use a very well padded counter top in case you slip, or the Vega slips, while taking it apart (towels, something very soft for the delicate circuitry when the backplate comes off)
2. Use a new, good quality #0 philips screw driver -- you'll need it to remove the tiny screws on the top, bottom, and shiny display port sides of the Vega case. Focus on the first quarter turn.
3. Start by securing the 4 metal risers with plastic O rings to the Morpheus II plate and use some Loc-tite on this. Leave it alone to dry while you disassemble the Vega.
4. Remove tiny top screws, then tiny bottom screws, shiny plate screws, and then easiest of all -- the screws on the actual back plate. Keep everything together in case you have to RMA or later resell.
5. Use a new straight edge razor to carefully remove the white sticker on the X GPU bracket. You need this sticker in one piece if you ever seek to RMA in the States.
6. Careful when cracking the Vega board away from the metal frame (after all screws have come out). You need to do this gently in order to access and separate the fan cable, and the cable that leads to the LED lights. Crack it only about half an inch and separate those two cables.
7. I use Q-tips + Acetone + 90% rubbing alcohol to clean the old crud off the GPU/hbcc die. There may be bits of thermal padding on the mosfets and chokes, and I clean that off as well. I place all the thermal pads onto the black metal frame in their appropriate indentations. I use magnification for this step. I spray canned air over the board when done to remove moisture and any residual crud.
8. Artic 5 Silver seems to work well. I apply to the Vega GPU/hbcc die and very lightly to the Morpheus II plate.
9. Take your time applying all those narrow heatsinks to the Mosfets. Note that even the low profile heat sinks will *not* fit the chokes that are located at the top of the GPU; the video kind of glides over this without explaining. You can put heat sinks on the side chokes.
10. Use books or something else to level up the bare, stripped down Vega board with the Morpheus II plate when lining up the new GPU brace and screwing that in. Otherwise, with all that thermal grease, the card will slide all over while you are trying to screw in the new GPU metal brace.
11. You could probably get by with (1) 120mm fan clipped to the fins over the GPU, but I would use (2) 120mm fans. Order some 1 to 3 fan cable splitters ahead of time.
12. Go into your bios and dial up your motherboard fan settings.
Carry the Vega + Raijintech cooler using the shiny display port front part and the back edge of the card, avoid touching the exposed back of the Vega.
Also, I found it easier to clip the (2) 120mm fans onto the Raijintech Morpheus fins *before* securing the Vega to the Morpheus II. Fan clips take a little while to get used to.
