Issue 50 is quite important, not only because this is where Wally gets his new costume but also because this is when he officially becomes as fast as Barry.
And issue 61 is one of the best issues from Messner-Loebs' run since it recaps a lot of the character work he did over the series. Is quite a great way to end an adventure as he would put it. (I seriously want to re-read his whole run right now).