Well.. I'm reluctant to clutter Brad's thread with non-Brad things...
Here's a few thoughts I have about iconic language. I'll not bother to support claim, as that's time-consuming and I don't know if you're interested. So here we go.
1. Every human language has a cultural aspect to it. In fact, I would say it's necessarily so. Cultural and semantic constraints are necessary for the operation of a language. In other words, iconic language is not a human language. I'm not saying that it's not useful, but the ultimate goal (human language) is not attainable at all in my eyes.
2. I'm not sure if you have, but it might be interesting for you to look into symbolic-note-taking done by simultaneous interpreters. The purpose of using symbols rather than language is to avoid language transfer effects.
3. I know a bit about sign language, but not tons. If you're interested in sign language in general, "The Signs of Language" by Klima and Bellugi is the place to start. If you're just interested in the speed, I don't have data. Sign language is really "flexible" in teh following way--speaking signers can speak and sign at the same time. Yet, since spoken language and sign language grammars / word sequences are different, the signing is sequenced based on the spoken language in this case. But it points to efficiency being comparable to that of spoken language. Also, sign-language simultaneous interpreting (from or to sign language) is also done regularly. These are not numbers, but just facts to use in the face of a lack of data (i.e. i don't have any)
4. Dr. Benjamin Bergen at UHawaii wrote an interesting paper on nativization effects in Esperanto. Cool paper. Maybe it might interest you. Maybe you've already read it. It's the only study on Esperanto that I could find.
I'll stop there for now; I gotta get back to my paper...
I'm not trying to flame or to puff my chest, but just to spit out a few opinions as fast as possible and see what interests you. Your thread on biology and behavior is exactly the same thread as I opened her previously. In other words, I think you're interested in a lot of the same things as I am, so I hope we can talk a bit in the future.
If you are interesteed in discussing this matter (iconic language), then I'd suggest to open a thread about it.
Peace,
Ben