I dunno if this is right or wrong, but I got 15lb mainline mono with a 40lb shock leader..making sure there are still a few coils of the leader around the spool just before cast, ensures the leader takes the strain of the cast, and the 15lb mono is easy to cast with a small diamiter..
Ive also read that if you use braid, it can sometimes slice through your finger on the cast, where as mono doesnt do this..
hope this helps,..
Matt