Best high-end graphics card price vs performance?

I was searching through old thread post and all the related topics I found were years old. Please correct me if this is something that's been hashed out here recently.

What's considered to be the best price vs. performance GPU setup these days? When watching the TeamPGP streams where they were borrowing a 1080ti, they kept mentioning that a pair of 1080s would perform better and ultimately be cheaper. That's still pretty pricey though. If you're the type of person who wants to run brand new games at 4k with good frame-rates and pretty high settings, what's the most cost effective way to achieve that goal? Is it a pair of cards in CrossFire or SLI, or just one beefy-ass card? What are the expectations for Vega so that it somehow fits into this equation? Does nVidia or AMD excel more at this performance-per-dollar benchmark these days?

The last time I seriously looked into this was when I upgraded my card in my rig from 2011 to keep it going a bit longer (2500k going strong, baby!) about a year and a half ago. I settled on an 8 gig R9 390 because of the sales going on at the time. Now I'm looking to build a new system at the end of the summer (late September), so these questions are starting to linger in the back of my mind.

Well it really depends from game to game really.
But i personally allways recommend to just go with a single higherend card,
over crossfire or sli two lower tier cards.
The reason being, that allthough with two semi highend cards you could see better performance in games that are well optimized to run dual gpu´s.
But you can allways have a hard time in games that dont particullary play well with dual gpu´s.
Allthough i do think that most modern AAA games nowdays, should work well with dual gpu´s.

Maybe not exactly what you´re looking for, don´t know.

The problem with depending solely on crossfire/SLI is that proper multi-gpu support has always been hit or miss. It takes effort by the developer to implement it correctly. Even more so with the new API's like DirectX 12 and Vulkan. It's great when it's done properly, not so great when it's not. Trying to use crossfire or SLI in game without proper support can make it a stuttering, unplayable mess.

All that being said, I have been running multi-gpu rigs since 2011. I try to base my build on a single gpu that will give decent performance at the resolution and frame rates that I want at the best price. Then add a second gpu to take advantage of games that have proper support so I can run those games at maximum setting at the highest frame rates that monitor will support. If multi-gpu support isn't there or doesn't work properly, I can always drop back to one gpu and adjust the games settings a little to keep the frame rates in the playable range but I probably won't hit the 100hz that my monitor supports.

Too me, crossfire/SLI doesn't hold up when discussing price vs performance for these reason. It's a nice to have option if you have the spare cash and you've built the rest of your system to accommodate multi-gpu's.