Lcdx has slightly more rumble and a smidge more qty(not much at all) the he4 has a snappier punch.
Lcd3f is even less deep and punchy than the x. The he4 is more aggressive and open than both but doesn't have the weight of tone either does.
I understand hemi... Not knocking the gd just saying that I doubt the he4 bass will ever be an he400 bass no matter what amp you throw it on. I think the he4 bass is good quality but its not satisfying to me without eq. The LCD x is barely there either.
The he4 won't ever have he400 bass, and that's ok with me since it destroys the he400 in every other aspect
grizz, definitely give pad rolling a chance. You'll be surprised. From the sounds of it, I feel like you would enjoy the 1540 pads. Definitely more rumbly than stock and only a little bit less air. Those NVX angled pads are very good as well, and you won't have to worry about losing air -- in fact they will even help the soundstage (maybe not as rumbly as the 1540's though, can't remember).
oooh I love 1540 pads. I may give it a crack!