Bear in mind that 2 specimens of the same species can vary in appearance. I have each of these, and my experience is:

'Aureocaulis': I have 2 of these and they are a nice, buttery yellow, with sharply defined green stripes. One, however, is a little paler yellow than the other. It has grown and sent out runners quite quickly. Remember that vivax is a thin-walled bamboo and can snap in half under snow loading. Probably the biggest and brightest, though.

'Robert Young': Can be slow to get established (mine took 3 years to start exhibiting much growth). Has lighter green leaves than the Aureocaulis. Unique, sulfury color, but not as pleasing to me as Aureocaulis.

'Holochrysa': Very nice, but will take longer to size up than the Aureocaulis.

Also, you should take a look at Ph. aureosulcata 'Aureocaulis' which can be quite impressive and is preferred by many people who are attracted to yellow-orange culms.

Vivax Aureocaulis will surely have the biggest but as Kudzu said, they are not really a bright yellow. Still, a stunning bamboo.

Now let me share an observation with you, most of the yellow culm bamboos that I've seen in hot & humid climates have culms that get covered with a black sooty 'something' that really mutes the yellow culms. You can rub it off but it is not really feasible to do on a large scale. I do not know what this stuff is but I do not think that it is sooty mold. Maybe it is sooty mold, but it does not affect the leaves, only the culms, and I have the impression that sooty mold (aphids & ants in combo cause this) makes the leaves quite gacky with black crud and the leaves on mine remain unaffected..

Your summer climate is similar to mine and mine have this problem so I would guess that you will also, as does bamboo in SW Tennessee - maybe I'm leaping to conclusions here but my gut tells me all hot & humid areas probably see this. It does seem to me that Robert Young, S Y Kimmeii and the Vivax Aureocaulis look much worse than Aureosulcata Aureocaulis or Spectabilis or Bambusoides Castillonis.

Hopefully Mike in Marietta can weigh in on this as he surely has yellow bamboo in his SC garden. Without this sooty stuuf, I would put in a hearty vote for the Vivax A in your situation, but if it is an issue, well I've always found photos of the Bambusoides Allgold/Holochrysa to be quite stunning and it may be less susceptible, I don't know.

I just thought I'd put this info out there for you to consider.

I have noticed the sooty mold problem here in the Pacific Northwest. I have experienced it myself and observed it at the the two large bamboo retailers here, Bamboo Garden and another I can't remember that is run by a Chinese man first name of Paul.
I removed my Ph Allgold for this very reason and would think twice before I got another yellow culmed bamboo.

I wasn't totally clear on my description either, I also see this on green culmed bamboo but it is way more apparent and detracting on the yellow guys and I think that folks should consider this when planting them.

I'd love to hear what others think this is as I am not convinced that it is sooty mold due to totally unaffected leaves, but I should start a new thread rather than 'popcorn' this one!

hoosier52-
I live in the PNW and I used to have the soot/mold problem with several bamboo (particularly Allgold, and sometimes Castillon and Robert Young) at my other house, but haven't had it this year at my new place. I moved in January from a lot with a lot of tall firs and partial shade to one that is open and sunny (at least as sunny as it gets here!). I also use Avid about once or twice a year for mite control and that might be helping (I have always assumed that it was a result of aphid secretions). Lastly, I have a lot of ladybugs here, and they like to munch on aphids. I don't know if all of those factors are contributing to the improvement, but I'm happy for the moment.

iandad- If you haven't already, you might want to peruse the photos at www.bambooweb.info to make some comparisons. Here's a picture of my Aureocaulis:

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This is a division from a grove that had a lot of 2" culms, and it's pretty impressive when it starts reaching and exceeding that size.

Thanks for all the input, especially the sooty mold comments.

Interestingly enough, my Alphonse Karr hedge does NOT seem to have any of this problem with sooty mold but my gardenias have to be cleaned up at least once a year.

Is there a consensus that the smaller diameter (yellow) culms are not as susceptible to this problem???

The sooty mold problem is definately caused by aphid secretions. Aphids this year were a nightmare in my part of the worlds. I wouldn't think culm size would have anything to do with it, it's just sweet, sticky aphid secretions that harbor and feed the black sooty mold.