I haven't read most of the authors here (this thread is doing double duty, being great for finding more authors/books to read, thanks) but from what I know so far, Egan is the best at writing about true immortality. Like trillions of years to actually infinite time level.
Diaspora (my favourite book) goes so far as to just stop counting time anymore because it just goes so unimaginably far.
http://www.gregegan.net/
https://www.wikiwand.com/en/Greg_Egan