Grave Lotus Combat Drug and Cluster Caltrops

Grave lotus probably only ups Reavers' base strength,
with Cluster Caltrops being resolved @unchanged strength 6, correct?

Correct. It doesn't even help the regular ones because blade vanes are always str4 rending. It makes all the regular attacks on the charge starting turn 4 str5 tho.

Imagine if we just HAD universal feel no pain so we started getting the good bonuses on turn 2. That would be so swell.

Hammer of Wrath specifically excludes any bonuses from Special Rules.

*Except special rules that explicitly modify Hammer of Wraith.

Dark Eldar Reavers Bladevanes
Dark Eldar Reavers Cluster Caltrops
Harlequins Embrace

That's all I've got off the top of my head.

You're right, HoW can't interact with Grave Lotus. It must be unmodified St: User unless specifically overridden by a special HoW rule as mentioned by @amorrowlyday.

I have a question of my own though, if you guys don't mind:

* Do HoW attacks still resolve at the I:10 Step if I assault through difficult terrain (which would of course normally override attacks to I:1)?

Doesn't seem to be specifically addressed either way but I'd say that Hammer of Wrath is an advanced rule and therefore overrides the basic rule of charging through terrain.

Thanks Count, that's certainly the answer I wanted.

The "...regardless of other Initiative modifiers" bit in the Charging Through Difficult Terrain section is my only worry. The HoW wording is "...at the Initiative 10 Step" rather than something like "...treat your Initiative as 10" though, so there's justification for it not being a modifier as such.

It doesn't modify your initiative, it grants you an extra attack at the I10 step.

Yep, agreed. Makes cluster caltrops all the more appealing.