The problem is very few places benchmark UWQHD or UWFHD. I've found that if it can run between 55-60fps at 4k it can run 90-100fps at 3440x1440 on the same settings.
As an owner of a Predator X34 I can tell you if you want to play on Ultra @100Hz you need a 1080 Ti.
60Hz you should be fine with a 1080.
If you're keen on getting a new 20 series, the 2080 would be nice to have, and the 2080 Ti would be the only thing that would give you solid frame rates with ray tracing turned on in upcoming titles but that's a lot of money to spend on technology that literally 2-3 games have.
Without ray tracing, a 1080 Ti or 2080 will be super solid and give 90-100fps in most upcoming titles on Ultra quality.
As of right now the only game my 1080...