Personally, I would stick to the normal Opera because I don't need the extra (gamer orientated) features.
But if you're a gamer or just like those extra features go for GX because under the hood it's the same browser.
Should You Use It?
If you love the look or want features like Razer Chroma and Twitch integration, then go ahead and use Opera GX. Despite the unusual look, this is a pretty standard Chromium browser that should work just like Chrome with websites.
That’s the main attraction here, however: The aesthetic and the built-in game culture features like Twitch integration and gaming news. The initial version of Opera GX even identifies its version number as “LVL 1.”
The limiters are one of the most interesting features we’ve seen in a browser in a while and could be worth playing with. Don’t expect huge performance increases, however. And watch out: If you leave those enabled all the time, you’ll just end up using a slower browser.
Opera just released “Opera GX” and advertises it as the world’s first gaming browser. Beyond the gaming-inspired theme and Razer Chroma integration, there’s a very interesting CPU and RAM limiter feature. But will it speed up your PC gaming?
I guess it's like anything else: demo each one. BUT, do you trust your perceptions? I'm into benchmarking but not browsers. The only one that comes close and is current is PCMark 10--Essentials Group which has a web browser test, it seems. I've run this before, it doesn't seem unduly strenuous. There's other stuff that comes up if you search but much of it is from 201-2013--a bygone era.
I always wondered whether gaming-oriented browsers could be more suitable for "potato" machines instead. Sticking w/regular Opera.