I wish I had multiple choices for reviewing. Here is a detailed review.
First, Avada is the most selling theme on themeforest BUT I was leaning towards X since the beginning. I was curios to try Avada as well. I got it and installed it. First thing I noticed is Avada's upload size is almost twice(~15MB) when compared to X theme(~8MB).
Also, since the moment I activated Avada, my admin got slow. I had deleted all plugins before evaluating. This tells enough that the output of the site would be slower as well. This was enough for me to stop my testing as I hate bloated stuff.
I like fast websites and even Google does(http://searchengineland.com/google-says-page-speed-ranking-factor-use-mobile-page-speed-mobile-sites-upcoming-months-250874).
Now coming to X theme part. Support is awesome. I faced issues in the beginning when they switched to email support but they came back to the forum support and the new support is awesome! I have got other themes as well and they limit support after asking one or two questions saying it is out of scope. With X, it is totally different. Without any performance plugin I got GTMetrix score of more than 85% which is awesome. Other themes I have tried have around 60% of score. So, I can say that X theme is good for speed. There is a learning curve. I doubted X in the beginning thinking it is overhyped, but now I feel it is not the case, I enjoy buiilding with X and consider it for future projects as well. Since nothing is pefect, I can say that this is 9/10. There should have been some options to easily customize a few things, like linking a column, etc, maybe some things are made in that way due to performance issues. But that is easily achievable doing a Google search. There is a facebook group as well with more than 10K members who are really helpful. And not to forget the extensions which we get with X. X is powerful in itself and then those extensions are a cherry on top. Thanks for the awesome theme!