I'm not a big fan of Lash, and think warptime is much better. I'm a fan of the I6 character killer that is the warptime prince.
As to the bikes, I find that they do always under perform, but draw SO much fire power that they make their points back in allowing everything else to remain untouched. In theory they zoom up and take out a land raider or something.
I currently use the noise marines as the sit at home unit, but include the rhino and power fist as "just in case" protection. I have found them useful against drop podding dreadnoughts or from the side annoyance. I have considered dropping the sonic blasters, but keep them for the rare kill point fight where sitting at home is less needed. I do agree that the doom siren could be good, and I will think about adding it. It would free up a few points that could provide some more fun.
Thanks for the comments.