If you upgrade to High Sierra and you find your Mac is slow with very poor fps then go to “About This Mac” and see what graphics card you are running. You may find that your high-end card is no longer working and your Mac has defaulted to on-board graphics or something. This is because many graphics cards are not supported by OS High Sierra (especially from the Nvidia range). Give it a week or so and I am told that Nvidia should be releasing their latest drivers for the new Mojave OS. This then should fix the issue once you update to the latest drivers in High Sierra.
Alternatively… Nvidia cards will run with Windows 7 and it is still supported by CCP. You can run Windows 7 from Bootcamp but you would then need to buy Windows 7 or better OS from Microsoft.
I am advised to wait a week or two and that is what I will be doing. I have High Sierra on my 2009 Mac Pro 4.1 and it is using my old 512Mb card to run it so I am using El Capitan (from my other drive) till the new drivers are released. Even with El Capitan I can still log in to Eve almost as normal (as stated above in previous threads). There really is no need to be buying new machines at this stage.
As a sidenote, I have also loaded Eve onto my High Sierra HDD and it runs with no issues but with horrible fps given the 512Mb card. Fingers crossed for the new drivers to come out soon.