Althought I haven't got the book yet (only read the previews), I'd say that all marine bolt-weapons are overpowered. Yes, it has been said that the boltweapons presented in DH and RT are civilian versions, but they still use same caliber ammo (perhaps the explosives are better, but still). I always had thought that only the weapons would get better with longer range, bigger clips and so on, not the damage jump so much. Not by giving them huge damagebonus.
I have used the bolter rules Luddite made a while ago with my DH Space Marine campaing, and I saw not much problem with it. OK, the bolts didn't tear enemies into two in one hit, but most ranged weapons aren't that lethal in 40kRPG as you would think.
But why then other weapons aren't given massive damageboost as well? Or, even better: why not balance all the weapons between DH, RT and DW (like in TT)? After all, isn't most of the technology standardised in the Imperium? It is certain that the SM should have better quality weapons, but not outright completely different weapons which just share their technology with the rest of imperial weapons.
(And this whole thing stinks of power creep to me)