OC'ing a Vega (on the right way) isn't so easy. It's simple to flash a Vega64 LC BIOS, but with exception of an explosion of your power consumption you get only a few percent more gaming performance. Undervolting, to break the power limitation, is the better way. You can keep the performance and save a lot of ressources. But exactly this thing is very difficult to realize. WattMan alone isn't able to realize such projects. And with a new driver this game starts again and again.
I tried it so often with now more than 10 cards - each card is so different and I was not able to found a global setting for all cards to write a recommendation. It makes no sense for me to write about an undervolting sensation for one card, if the next card was a potatoe chip. I have here both extreme, good and bad chips. And if you see this big bandwidth, you can understand me, why I dislike such OC or UV parts in a review.
Spoiler:
I'm just testing the Gigabyte RX Vega64 Gaming OC and it is interesting to see, that Gigabyte is very well knowing the limitations of their cooling solution. The power draw is very similar and I really like this bigger card. But it is nothing for a big OC. If you need significant more performance (f.e. in Ultra-HD), Vega is the wrong horse. But for WQHD and Freesync it is a very good offer.
I've played Wolfenstein 2 with a water cooled Vega64 (full-cover water block) in Ultra-HD and was satisified - but to finish now Witcher 3 for a 100% savegame (story), it was totally unusable. I also tried to OC this Vega64 and got stable 1,7 GHz - but this was also not enough for a good immersion. The advantage of an open loop cooling system and quick connectors is, that I can change the cards within five minutes. The 1080 Ti was is this case the significant better solution. This is, what I meant above with the horse. It differs from case to case