As big as you want but it is not always practical.
All around performance, and easiest fit without changing things in the engine bay too much, is the 5.0L.
There have been a ton of these done but on an ’04 not sure !
Review all of the How To’s and the Threads on the subject, then decide if the swap is good for you.
Now as far as a stroked 5.0L, you can go to 347 CI even from Ford.