Faster way of reading csv to grid
What's the use of presenting even 5,000 records to the user? Do you expect a user to scroll to row 4711, look at "18912,N", and say "Strange, why wasn't there a '12345,N' in row 1234?", or "Interesting, now let's see where the corresponding '54321,X" is to be found!"?

Your GUI should help the user to specify the comparatively small set(s) of records pertinent to his current problem/question; even if working with the data means "check every item in turn", it would be more human to present the records in small batches.

All this points to using your file as a database table bound to the controls of your GUI; then the problem of "reading a .csv fast" completely vanishes.