Ah. I have a 1080 ti. With the 27" Predator 1440, I never had any issues with fps and could max out most of the newer titles and never go below 60. I would think going to curved and wide at the percentage increase you mentioned wouldn't hurt me too bad.
A 1080Ti is a very strong GPU.
Going from 1440 16:9 to 1440 21:9 (if I'm following you correctly) is a jump, at ~34%. Though the 1080Ti should be OK, it would probably be good to do a little research to be clear how much the difference might be.
I hope this makes sense.EDIT: I read your current res wrong and had to correct it Edit 2...retracted my inaccurate assertion regarding 4k. Sorry for any confusion.