I’ve just read your article and was asking myself about the concurrent_insert variable. According to me the default behavior (concurrent_insert=1) allows concurrent insert if the myisam table is not fragmented, in that case inserts can be performed at the same time that SELECT statements are reading rows from the table :
http://dev.mysql.com/doc/refman/5.1/en/concurrent-inserts.html

So in your case can we really say that the SELECT would be blocked during the 3 seconds INSERT ?