I agree with previous comments - the 29mm legs of the Manfrotto are inadequate for the 500/4. The same would be true of a Gitzo Series 2. In other words, it's not the wrong the brand, but the wrong leg diameter.
Of course, Manfrotto does not make a larger diameter CF tripod. The perfect tripod (from a stability point of view) would be a Series 5 but a Series 3 (as I use) will do the job. Same thing Dave and Joe suggested. The 3 of us are using more or less similar lenses (Dave's 400/2.8 a bit tougher) and I think all seeing the same thing.
I would guess that the problem with your 055 is that when you use your left hand to stabilize the lens, the view is still shaking. That is because the tripod is simply not rigid enough to stabilize the lens, or even to "support" your hand, if that makes sense.
You can see this in an objective way with the tap test, which Joe mentioned. My guess is that when you tap the lens the view is wild and loose and takes a long time to settle (well over 5 seconds), if it ever really settles outdoors where there is usually some breeze, even if light. That is what I experienced with my G1228. A GT2541 would perform better than my G1228 but it would not solve the problem.
in other words, I don;t think it matters where you put your hand because you can't solve the tripod problem.
The RRS Long Lens Support (LLS) will not help for two reasons:
1. The LLS cannot stop the flex happening underneath the tripod foot, and that flex is the mount, the legs, etc. The LLS can only improve one thing, and that is any flex introduced by the lens foot or collar. If you study the images of the Long Lens Foot on RRS's site I think this will make a lot of sense. The LLS is simply taking some stress off the lens foot/collar. That's it.
2. I have only used the LLS on my 500/4 AFS. This is the original AFs with the metal (not CF) lens barrel, and of course without VR. Interestingly, it weighs about the same as your VR model, apparently the VR weighs about as much as the reduction in lens barrel weight by using CF on the barrel.
I use the LLS whenever possible. I find it quite annoying in some ways. It makes the tripod quite a bit bulkier when I fold it up for transport in my vehicle and the LLS is always attacking something else in my vehicle .
It raises the center of gravity of the lens by about an inch. On a Wimberly without a flash mounted that is no big deal because the clamp platform is just adjusted to a different height. But when using a Wimberly flash bracket with on extension I need the center of gravity as low as possible in order to better balance things with the flash hanging 10" over the lens. And then the Wimberly platform does not go as low as I would like. I don't consider that a design problem with the gimbal but more a general problem with balancing a high flash.
It is difficult or impossible to use with my ThinkTank Hydrophobia, which is more important to me now then anything the LLS might do. The Hydrophobia is a true game changing accessory. I shoot without fear in weather I would never shoot in or might blow off for fear of getting caught out on the trail away from my vehicle in a sudden summer storm... that kind of thing.
Most importantly, the LLS absolutely, positively must be used with an RRS lens foot, or likely a Wimberly plate would work (I think I've tested my P40 plate). The double sided screw clamp on that thing is far more sensitive to plate width than even the RRS lever clamp. And even with an RRS plate I would never use it without stop pins. I find that double sided clamp quite scary .
For some reason I cannot divine, the camera bar on the LLS does not come with a stop pin for the rear side. The front side has a natural stop created by the Y support. I called RRS about that and they gave me an absolutely senseless answer and that phone call in itself was quite a story and reduced my opinion of the company. It was that senseless.
Anyway... I cut down a standard 1/4-20 bolt to the exact height I wanted and screwed that into an available hole at the back end of the camera bar. The bolt was sized to stick out at the same height as a standard RRS stop pin and therefore slides into the Wimberly clamp's stop pin slot.
I may be anal about stop spins but I think that thing just screams for a stop pin. Especially because you end up with two closely adjacent screw clamp knobs. It would be easy to grab and loosen the wrong knob, for example. The whole setup is quite a monstrosity.
Those are all the bad things I found with the LLS.
On the positive side, I found it helps... a little. A very little. It is not in any way a game changer. It won't make a Series 3 act like a Series 4 or 5. I often question if the bad things are worth the little extra stability I get.
I do not know how much, if any, the various long lens collars vary in terms of rigidity. Bkorn Rorslett has long been a critic of various Nikon lens feet and I think he came to the conclusion that the feet and collars have been lightened up over succeeding models (presumably to reduce weight). Recently Thom Hogan has been critical of certain long lens feet and started recommending the LLS.
What I'm trying to say is that my experience with my now rather old lens may be different than that experienced with other lenses. But if other lenses respond better to the LLS then my lens must be showing me the true stability of the tripod, and in that case I know that something mroe than a Series would help, especially without VR.
One other interesting benefit of the LLS. In principle these lenses should always be shot with the collar locked down. But then it adds time required to rotate into a portrait mode shot or just to level a tilted horizon. And since I move about a lot during the day, I rarely take the time to level my mount so I need to constantly tweak the horizon.
With the LLS, I set a lot of tension on the front end Y support, and that allows me to shoot with the collar loose, but still with tension on the collar. And that alone might be worth the various prices of admission .
In summary, that lens needs more tripod and there is nothing you can do to significantly change that. The LLS won't solve the problem, nor will adding weight.
I'll close by saying that I recently tap tested an 80-400 (working 400mm) and a 300/4 working 500mm on an 055. Although both those lenses ideally should be shot on 32mm legs, I was very impressed with the performance of the 055. It's a good tripod, it is just under-powered for your lens. I think it was the CF version, but this was a couple of months ago and now I'm unsure. I actually tried two different 055 tripods, both being side by side, each with one of those two lenses.