5760x1200 is 6,912,000 pixels, which is 1 billion less pixels than true 4k resolution (3840×2160, 8,294,400 pixels), so 4k framerates could be comparable to 5760x1200 framerates (but take it with a grain of salt, as for ultrawide resolutions like 5760x1200 the GPU would need more memory to load textures).
So it might be worth to get two GTX 1080 Ti and use them in SLI - according to benchmark they will outperform 2080 Ti for almost the same cost:
https://www.youtube.com/watch?v=WiK0bomLrvM
That is unless you want to throw money and get two 2080 Ti in SLI - nothing would beat it, but you would spend $1000 more for a marginal increase in performance (and a chance of getting a faulty GPU, since Nvidia's 20xx series were having a lot of troubles and bad chips).
You should also consider upgrading your RAM and SSD to max out your rig performance, to something like this Intel Optane in RAID 0 https://www.newegg.com/Product/Product.aspx?Item=N82E16820167440 for storage and at least 32 GB of RAM either at 4133MHz and 17 CAS latency like this G.SKILL F4-4133C17Q-32GTZR https://www.newegg.com/Product/Product.aspx?Item=N82E16820232677 or this 4700MHz Corsair CMW16GX4M2K4700C19 https://www.newegg.com/Product/Product.aspx?Item=N82E16820236447 and also investing in custom professional liquid cooling for your rig, as this will allow you to OC your GPU's and CPU even more.