Pretty much putting LRMs on everything of mine now. Standard Engine and medium lasers are for brawling, and the LRM15s are to soften them up before you reach them. JJs are for getting around rough terrain, and some extra maneuverability.
Run LRM30 (20+10) on the 5S. http://www.mechspecs.com/forum/index.php?topic=4169.0 e.g. You got a bigger Launch Volley and so a bigger Strike plus more Missiles. On the 9SE i would recommend to go Brawler Builds with Lasers and S(S)RMs.
I really, really wouldn't use a 260 engine in a Thunderbolt. It makes it as slow as an assault without either the armour or the firepower to compensate for it.