So I think I put in a compromise.  I kept the original 10^4 example for reading in a file in the code, but added a markdown code block at the end of the section using an example with 10^8 rows.  This file is ~1.8 GB and takes more than 8 minutes to read in off my SSD with read.csv() vs less than 10 sec for fread().  I put these stats in to the Rmd to illustrate the point, but then students/instructors won't have to run it live.