I just got done moving myself, now i'm playing the waiting game for the tanks to arrive! Leave it to the one day i'm flying across the country for an Iwagumi thread to pop up. Anyway, enough of that, lets roll up the sleeves and get to work.
First observation - EVERY Iwagumi aquascaper on the face of the planet that at least knows the basic concept of what they're doing is almost never satisfied with their rocks. Take solace in the fact that your anguish is shared amongst the rest of us Iwagumi scapers to an almost masochistic extreme. The quest for better stones is a never ending endeavor. However, you do have a good selection to work with, so take heart.
As for the aquascape, you have good instincts, listen to them. in terms of Iwagumi design and rules #4 of the day one set was indeed your best composition, and I will explain why.
#1 Has potential - and is probably your second best aquascape of the fold (from day 1), because it uses the texture of the rock to it's advantage to create a mountainscape (which Manten is more mountainesque than say, rugged coastline or jagged cliff). However you need to have the rocks be more present - they'd get engulfed by plants the second they were planted, so you'd need to maintain the height, and lessen the soil to emphasize the stone placement - otherwise you'd have ended up with a mound of plants and forgot that the rocks are even there.
#2 as blair pointed out is moving too much in one direction - which works sometimes, but not in this case. Here it just throws off the balance. Also, the stones are kind of used in a similar fashion to how you would use, say Shou or other slate-like stones. This causes the manten stones to be placed at weird angles that just doesn't fit right with the feel of the stones (as I mentioned earlier, they aren't so much the jagged look). Usually 'points' used in Manten stones are reserved only for the main and main support stones to create impressions in the way the rock might naturally fall. Basically, the striaght edges of your stone works against you.
#3 is too low - there is too much open space above the rocks that de-emphasize their presence in the scape (which is very important in a rock only aquascape), they're simply not set high enough (or not big enough) to make much of an impact in the long run. Also, as blair mentioned, they are crowded together too aggressively, which when I look at it, it's hard to discern which stone is the main stone (since all the stones are on an even height level just about, and blended together too well), without the prior knowledge of which stone you've been actively using as your main stone. However it is a step in the right direction.
#4 hit the whammy. #4 is a very good layout choice for the feel of manten stone, to me it looks almost instantly balanced as far as initial placement and soil work is concerned and I can instantly discern where the main stone is. The space in front of the main stone area also serves as a good focal area to emphasize a section of the carpet, and it seems like the shadows would work to your advantage when the lighting is used. However, there are a few adjustments, first you need more soil, the main hill has to be higher up to avoid the "too much" open space up top syndrome, which as previously stated would understate the impression of the stonework. It's a very common error to not have enough appropriate height in an Iwagumi layout, so don't fret it too much (in fact in some of my aquascapes i've gone the opposite way and had -too much- height in the layout). Also the stone in the left back should not be at the same height as the main stone. Think of it this way: The main stone is the alpha male lion, the main support stones are the female lions, and the small support stones are the cubs. Now, the cubs have -zero- business toying around or even pretending they're of the same calibur as the alpha male, and have to be submissive to the alpha. The female lions, act as the primary support network for the alpha by hunting and providing more cubs for the pride - ergo they've earned the right to be in the immediate presence of the alpha and at -almost- an even keel with the alpha, but still not quite, they're still lower.
The other thing to adjust, is to try to show us other faces of the main stone, while in the same position it's in now, i'm sure that rock has a more personable side it's dying to show us and bring the scape together. Past that it would come down to basically making small adjustments in the spacing between the stones and their basic positionings and angles. But I think this one has the most hidden potential. As a side note, #9 from your recent scapes does has potential too, and I think it's your best scape from day 2, but whether to work iwth #4 or #9 is dependent on what kind of impression you want to give off - #4 is more about balance and stability, #9 is more about domination.