It took me a year to decide and order a reader. Still haven't received it.
Those pdf's probably won't look great on any small reader.
Have you looked at the beebook neo/onyx boox. They do fit a lot of your requirements and their firmwares are interchangeable.
It has a wacom touchscreen which doesn't affect screen clarity like the touchscreen on the sony.
It has probably the best pdf support currently available on a 6" including various zoom options. And it memorizes the zoom when changing the page.
There are games available for it like hangman, battleship, minesweeper, sudoku, chess and more.
It has wifi so you get your wikipedia also.
It even has tts support according to the web page but since I'm not interested in tts I never checked into the quality of it.
And it supports chm.
But if most of your reading is complicated pdf's I would look into a larger reader like irex 800 or bigger.