Taken from PC Gamer site:
As far as just simply gaming goes, 16GB is plenty, and really, you can get by just fine with 8GB. In a handful of gaming performance tests, Techspot foundbasically no difference between 8GB and 16GB in terms of framerate. In their tests, GTA V (9GB RAM total usage) plus 65 open Chrome tabs (2.2GB usage) performed at 56 fps with both 16GB and 8GB RAM configurations. Similarly, Batman: Arkham Knight (9.8GB total usage) plus the same 65 Chrome tabs pulled 102 frames at 16GB and only dropped to 101 with 8GB.
In general, more RAM can make your computing more pleasant, and we certainly don't recommend against 32GB. But if you're looking for the best way to improve framerate, a better video card is going to make a much bigger difference than going from 8GB to 32GB, which may have no effect at all.
RAM is a nice bonus, but your graphics card and cpu are going to have a much stronger impact on gaming experience. If you want to splurge on something that can improve the overall gaming experience, being able to have your game(s) on an SSD can be a nice boost when things are loading, etc.
Both memory and video card prices are at the worst they've been, ever. This is a terrible time to upgrade a system if you don't really need it. I would suggest sitting on the decision for awhile and see what happens. Pantheon is many months from release and a lot could happen in that time.
A game like Pantheon should play well with an i5 with 8 GB of RAM if you have a middle of the road video card (ie NVidia 1060) so long as you're not thinking of extreme monitor resolution like 4K.
As Celandor has stated, both RAM and GPU (video card) priced have sky rocketed in the last year (thanks to crypto currency mining) Its best to wait until the next generation and grab the new cipsets quickly before the price is inflated by the miners. :D
I wanted to build a new system this year but the miners inflated the demand / prices and made it near impossible to justify the price point.