FC5 doesn't hit 100 FPS on a 2080Ti, I know that for sure. Shadow of the Tomb Raider is another rather demanding game I tested nowadays, which sits around 80 (with a decent overclock and 130% power target).
I think for 60 it might work, but 100 is far from reality. Compared to 1440p 16:9 (2560x1440), there are ~34% more pixels to render, which is a lot of load on the GPU.
If you pick a 2070 or RX5700 and going with 1080p, you're certainly way above 90 FPS. My 1070 in my other computer does 120 fine on my TV at 1080p.
I didn't mean to attack you, just to provide a realistic picture. However, that wasn't even the question, and I sadly can't answer the question either because I don't have the monitor. My TV behaves strangely for example: I can go 4k 60Hz, I can go 1080p 120Hz, but I can't go above 30Hz at 1440p. Weird stuff. The question whether you can set it to 2560x1080 and still have the 100Hz available is reasonable. Sorry for not providing an answer @OP